ALSA: aloop: Fix Oops while PM resume

commit edac894389f9c9de2a1368c78809c824b343f3a5 upstream.

snd-aloop driver has no proper PM implementation, thus the PM resume
may trigger Oops due to leftover timer instance.  This patch adds the
missing suspend/resume implementation.

Reported-and-tested-by: El boulangero <elboulangero@gmail.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>