Staging: lirc, fix NULL dereference

When 'context' allocation fails in imon_probe, we jump to unlock
context->ctx_lock. This is wrong as context is NULL and the lock is
not locked.

Fix the labels.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Cc: Jarod Wilson <jarod@redhat.com>
Cc: Mauro Carvalho Chehab <mchehab@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>