intel_sst: MRST can only do 16bit recording

Fix bug

	$ arecord -D dsnoop -r 48000 -f S16_LE 1.wav
	ALSA lib pcm_direct.c:980:(snd1_pcm_direct_initialize_slave) unable to install hw params
	ALSA lib pcm_dsnoop.c:604:(snd_pcm_dsnoop_open) unable to initialize slave
	arecord: main:654: audio open error: Interrupted system call

Root cause is, the driver is reporting 32-bit capture capability
that is not supported by the MRST hardware. So the dsnoop plugin
end up requesting 32-bit capture which fails.

Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
Signed-off-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>