ALSA: hda/ca0132 - Fix possible NULL dereference

Spotted by smatch,
  sound/pci/hda/patch_ca0132.c:1950 dspxfr_image() error: potential
  null dereference 'dma_engine'.  (kzalloc returns null)
  sound/pci/hda/patch_ca0132.c:1950 dspxfr_image() error: we
  previously assumed 'dma_engine' could be null (see line 1857)

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>