ALSA: ctxfi: Fallback DMA mask to 32bit

Currently ctxfi driver tries to set only the 64bit DMA mask on 64bit
architectures, and bails out if it fails.  This causes a problem on
some platforms since the 64bit DMA isn't always guaranteed.  We should
fall back to the default 32bit DMA when 64bit DMA fails.

Fixes: 6d74b86d

 ("ALSA: ctxfi - Allow 64bit DMA")
Cc: <stable@vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>