soundwire: stream: remove useless initialization of local variable

no need to reset return value.

Detected with cppcheck:
[drivers/soundwire/stream.c:332]: (style) Variable 'ret' is assigned a
value that is never used.

Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Reviewed-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Vinod Koul <vkoul@kernel.org>