ALSA: timer: Fix wrong instance passed to slave callbacks

ALSA: timer: Fix wrong instance passed to slave callbacks

commit 117159f0b9d392fb433a7871426fad50317f06f7 upstream.

In snd_timer_notify1(), the wrong timer instance was passed for slave
ccallback function.  This leads to the access to the wrong data when
an incompatible master is handled (e.g. the master is the sequencer
timer and the slave is a user timer), as spotted by syzkaller fuzzer.

This patch fixes that wrong assignment.

BugLink: http://lkml.kernel.org/r/CACT4Y+Y_Bm+7epAb=8Wi=AaWd+DYS7qawX52qxdCfOfY49vozQ@mail.gmail.com
Reported-by: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>