intel_sst: MRST can only do mono recording

Fix bug

	$ arecord -Dplughw -c2
	Recording WAVE 'stdin' : Unsigned 8 bit, Rate 8000 Hz, Stereo
	arecord: set_params:1116: Unable to install hw params:
	ACCESS:  RW_INTERLEAVED
	FORMAT:  U8
	SUBFORMAT:  STD
	SAMPLE_BITS: 8
	FRAME_BITS: 16
	CHANNELS: 2
	[...]

Root cause is, the driver is reporting 2-channel capture capability
that is not supported by the MRST hardware. So the plughw plugin
end up requesting 2-channel 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>

drivers/staging/intel_sst/intelmid.c

@@ -335,6 +335,13 @@ static int snd_intelmad_open(struct snd_pcm_substream *substream,
 	runtime = substream->runtime;
 	/* set the runtime hw parameter with local snd_pcm_hardware struct */
 	runtime->hw = snd_intelmad_stream;
+	if (intelmaddata->cpu_id == CPU_CHIP_LINCROFT) {
+		/*
+		 * MRST firmware currently denies stereo recording requests.
+		 */
+		if (substream->stream == SNDRV_PCM_STREAM_CAPTURE)
+			runtime->hw.channels_max = 1;
+	}
 	if (intelmaddata->cpu_id == CPU_CHIP_PENWELL) {
 		runtime->hw = snd_intelmad_stream;
 		runtime->hw.rates = SNDRV_PCM_RATE_48000;