input: cyttsp_button: fix kernfs_path() usage

In the msm8996 kernel, the kernfs_path() function has an updated signature
that returns int instead of char *, which breaks compilation of the
cyttsp_button driver. This patch updates the code to properly handle the
new signature by passing a buffer and checking the return value.

Signed-off-by: Onelots <onelots@onelots.fr>

drivers/input/touchscreen/cyttsp_button.c

@@ -1183,36 +1183,47 @@ static const struct attribute_group cyttsp_attr_group = {
 
 static int cyttsp_proc_init(struct kernfs_node *sysfs_node_parent)
 {
-	int ret = 0;
-	char *buf, *path = NULL;
-	char *reversed_keys_sysfs_node;
-	struct proc_dir_entry *proc_entry_buttons = NULL;
-	struct proc_dir_entry *proc_symlink_tmp  = NULL;
+    int ret = 0;
+    char *buf, *path = NULL;
+    char *reversed_keys_sysfs_node;
+    struct proc_dir_entry *proc_entry_buttons = NULL;
+    struct proc_dir_entry *proc_symlink_tmp  = NULL;
 
-	buf = kzalloc(PATH_MAX, GFP_KERNEL);
-	if (buf)
-		path = kernfs_path(sysfs_node_parent, buf, PATH_MAX);
+    buf = kzalloc(PATH_MAX, GFP_KERNEL);
+    if (buf) {
+        ret = kernfs_path(sysfs_node_parent, buf, PATH_MAX);
+        if (ret >= 0)
+            path = buf;
+        else {
+            pr_err("%s: kernfs_path() failed\n", __func__);
+            kfree(buf);
+            return ret;
+        }
+    } else {
+        pr_err("%s: Failed to allocate buffer for path\n", __func__);
+        return -ENOMEM;
+    }
+    proc_entry_buttons = proc_mkdir("buttons", NULL);
+    if (proc_entry_buttons == NULL) {
+        ret = -ENOMEM;
+        pr_err("%s: Couldn't create buttons\n", __func__);
+    }
 
-	proc_entry_buttons = proc_mkdir("buttons", NULL);
-	if (proc_entry_buttons == NULL) {
-		ret = -ENOMEM;
-		pr_err("%s: Couldn't create buttons\n", __func__);
-	}
+    reversed_keys_sysfs_node = kzalloc(PATH_MAX, GFP_KERNEL);
+    if (reversed_keys_sysfs_node) {
+        snprintf(reversed_keys_sysfs_node, PATH_MAX, "/sys%s/%s", path, "reversed_keys");
+    }
+    proc_symlink_tmp = proc_symlink("reversed_keys_enable",
+            proc_entry_buttons, reversed_keys_sysfs_node);
+    if (proc_symlink_tmp == NULL) {
+        ret = -ENOMEM;
+        pr_err("%s: Couldn't create reversed_keys_enable symlink\n", __func__);
+    }
 
-	reversed_keys_sysfs_node = kzalloc(PATH_MAX, GFP_KERNEL);
-	if (reversed_keys_sysfs_node)
-		sprintf(reversed_keys_sysfs_node, "/sys%s/%s", path, "reversed_keys");
-	proc_symlink_tmp = proc_symlink("reversed_keys_enable",
-			proc_entry_buttons, reversed_keys_sysfs_node);
-	if (proc_symlink_tmp == NULL) {
-		ret = -ENOMEM;
-		pr_err("%s: Couldn't create reversed_keys_enable symlink\n", __func__);
-	}
+    kfree(buf);
+    kfree(reversed_keys_sysfs_node);
 
-	kfree(buf);
-	kfree(reversed_keys_sysfs_node);
-
-	return ret;
+    return ret;
 }
 
 static int cyttsp_button_pinctrl_init(struct cyttsp_button_data *data)