staging: most: fix aim-sound build errors

staging: most: fix aim-sound build errors

Fix build errors: driver uses snd_pcm*() interfaces, so select
SND_PCM.

drivers/built-in.o: In function `audio_rx_completion':
sound.c:(.text+0x3cd376): undefined reference to `snd_pcm_period_elapsed'
drivers/built-in.o: In function `pcm_prepare':
sound.c:(.text+0x3cd3b0): undefined reference to `snd_pcm_format_physical_width'
sound.c:(.text+0x3cd3ce): undefined reference to `snd_pcm_format_big_endian'
sound.c:(.text+0x3cd42c): undefined reference to `snd_pcm_format_big_endian'
drivers/built-in.o: In function `pcm_hw_free':
sound.c:(.text+0x3cd50a): undefined reference to `snd_pcm_lib_free_vmalloc_buffer'
drivers/built-in.o: In function `pcm_hw_params':
sound.c:(.text+0x3cd54c): undefined reference to `_snd_pcm_lib_alloc_vmalloc_buffer'
drivers/built-in.o: In function `playback_thread':
sound.c:(.text+0x3cd6a0): undefined reference to `snd_pcm_period_elapsed'
drivers/built-in.o: In function `audio_probe_channel':
sound.c:(.text+0x3cdc0b): undefined reference to `snd_pcm_new'
sound.c:(.text+0x3cdc2b): undefined reference to `snd_pcm_set_ops'
drivers/built-in.o:(.data+0x952d0): undefined reference to `snd_pcm_lib_ioctl'
drivers/built-in.o:(.data+0x95318): undefined reference to `snd_pcm_lib_get_vmalloc_page'

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Acked-by: Christian Gromm <christian.gromm@microchip.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>