ALSA: ctxfi: Fix the incorrect check of dma_set_mask() call

In the commit [15c75b09: ALSA: ctxfi: Fallback DMA mask to 32bit],
I forgot to put "!" at dam_set_mask() call check in cthw20k1.c (while
cthw20k2.c is OK).  This patch fixes that obvious bug.

(As a side note: although the original commit was completely wrong,
 it's still working for most of machines, as it sets to 32bit DMA mask
 in the end.  So the bug severity is low.)

Fixes: 15c75b09 ("ALSA: ctxfi: Fallback DMA mask to 32bit")
Cc: <stable@vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>