ASoC: SOF: Propagate sof_get_ctrl_copy_params() error properly

This fixes a compile warning below by properly handling the error code
from sof_get_ctrl_copy_params():
  include/linux/kernel.h:843:43: warning: 'sparams.pl_size' may be used uninitialized in this function [-Wmaybe-uninitialized]
  sound/soc/sof/ipc.c:639:34: note: 'sparams.pl_size' was declared here

The function returns an error before setting sparams.pl_size, so it'd
assign an uninitialized value at a later point.

Fixes: 53e0c72d

 ("ASoC: SOF: Add support for IPC IO between DSP and Host")
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Mark Brown <broonie@kernel.org>