ALSA: spi: Drop superfluous PCM preallocation error checks

snd_pcm_lib_preallocate_pages() and co always succeed, so the error
check is simply redundant.  Drop it.

Reviewed-by: Jaroslav Kysela <perex@perex.cz>
Signed-off-by: Takashi Iwai <tiwai@suse.de>