ALSA: pcm: Return 0 when size < start_threshold in capture

ALSA: pcm: Return 0 when size < start_threshold in capture

[ Upstream commit 62ba568f7aef4beb0eda945a2b2a91b7a2b8f215 ]

In __snd_pcm_lib_xfer(), when capture, if state is PREPARED
and size is less than start_threshold nothing can be done.
As there is no error, 0 is returned.

Signed-off-by: Ricardo Biehl Pasquali <pasqualirb@gmail.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Stable-dep-of: 4413665dd6c5 ("ALSA: usb-audio: Add quirks for Dell WD19 dock")
Signed-off-by: Sasha Levin <sashal@kernel.org>