Use audio_channel_mask_t consistently

Change-Id: Ib832c0b707b1e0b82adf4ab3d4d18a2dc459d240
diff --git a/modules/audio/audio_hw.c b/modules/audio/audio_hw.c
index d860437..15e9920 100644
--- a/modules/audio/audio_hw.c
+++ b/modules/audio/audio_hw.c
@@ -55,7 +55,7 @@
     return 4096;
 }
 
-static uint32_t out_get_channels(const struct audio_stream *stream)
+static audio_channel_mask_t out_get_channels(const struct audio_stream *stream)
 {
     return AUDIO_CHANNEL_OUT_STEREO;
 }
@@ -148,7 +148,7 @@
     return 320;
 }
 
-static uint32_t in_get_channels(const struct audio_stream *stream)
+static audio_channel_mask_t in_get_channels(const struct audio_stream *stream)
 {
     return AUDIO_CHANNEL_IN_MONO;
 }