staging: bcm2835-audio: Fix incorrect draining handling

The handling of SNDRV_PCM_TRIGGER_STOP at the trigger callback is
incorrect: when the STOP is issued, the driver is supposed to drop the
stream immediately.  Meanwhile bcm2835 driver checks the DRAINING
state and tries to issue some different command.

This patch straightens things a bit, dropping the incorrect state
checks.  The draining behavior would be still not perfect at this
point, but will be improved in a later patch.

Signed-off-by: Takashi Iwai <tiwai@suse.de>
Tested-by: Stefan Wahren <stefan.wahren@i2se.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>