ALSA: vx: Don't try to update capture stream before running

[ Upstream commit ed3c177d960bb5881b945ca6f784868126bb90db ]

The update of stream costs significantly, and we should avoid it
unless the stream really has started.  Check pipe->running flag
instead of pipe->prepared.

Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Sasha Levin <alexander.levin@verizon.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>