asoc: Reset the buffer if size is partial or zero

Sometimes during device switch in recording,
observe size 0 is return from DSP due to EOS
handling. For ALSA pcm_read to unblock, buffer
appl_ptr is elapsed without actually updating
the buffer. And userspace copies the stale
data(old buffer) causing issue sometimes.
Reset the buffer for that period_size in
such cases instead of transfer stale data.

Change-Id: I0d3ac133a8d95fad0710586e3e947410a41c9c5a
Signed-off-by: Laxminath Kasam <lkasam@codeaurora.org>

techpack/audio/asoc/msm-pcm-q6-v2.c

@@ -953,6 +953,11 @@ static int msm_pcm_capture_copy(struct snd_pcm_substream *substream,
 			goto fail;
 		}
 
+		if (size == 0 || size < fbytes) {
+			memset(bufptr + offset + size, 0, fbytes - size);
+			size = xfer = fbytes;
+		}
+
 		if (copy_to_user(buf, bufptr+offset, xfer)) {
 			pr_err("Failed to copy buf to user\n");
 			ret = -EFAULT;