staging: most: Use managed buffer allocation

staging: most: Use managed buffer allocation

Clean up the driver with the new managed buffer allocation API.
Also remove the unnecessary checks of channels in hw_params callback
as this is guaranteed by the hw constraints in anyway.
After these cleanups, the hw_params and hw_free callbacks became
empty, hence dropped.

Signed-off-by: Takashi Iwai <tiwai@suse.de>
Link: https://lore.kernel.org/r/20191210141356.18074-2-tiwai@suse.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>