ALSA: ca0106 - Fix the max capture buffer size

The capture buffer size with 64kB seems broken with CA0106.
At least, either the update timing or the DMA position is wrong,
and this screws up pulseaudio badly.

This patch restricts the max buffer size less than that to make life
a bit easier.

Signed-off-by: Takashi Iwai <tiwai@suse.de>
Cc: <stable@kernel.org>