[ALSA] Fix possible deadlocks in sequencer at removal of ports

Fix possible rwsem deadlocks in sequencer code at removal of
sequencer ports.  The list_lock of port group can be double
locked.

Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Jaroslav Kysela <perex@suse.cz>