ALSA: line6: Fix -EBUSY error during active monitoring

ALSA: line6: Fix -EBUSY error during active monitoring

commit 4d0e677523a999e1dec28e55cc314c47ba09ca12 upstream.

When a monitor stream is active, the next PCM stream access results in
EBUSY error because of the check in line6_stream_start().  Fix this by
just skipping the submission of pending URBs when the stream is
already running instead.

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=101431
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>