staging: most: fix pcm_write input/output error

This patch keeps the process from sleeping after the PCM middle layer has
stopped playback by calling the pcm trigger callback. The patch is needed
to prevent aplay from causing a pcm_write Input/Output error.

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