staging: bcm2835-audio: Drop useless running flag and check

The running flag of alsa_stream is basically useless.  The running
state is strictly controlled in ALSA PCM core side, hence the check in
PCM trigger and close callbacks are superfluous.

Also, the prefill ack at trigger start became superfluous nowadays
with the ALSA PCM core update.

Let's rip them off.

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>