quota: Check for register_shrinker() failure.

quota: Check for register_shrinker() failure.

register_shrinker() might return -ENOMEM error since Linux 3.12.
Call panic() as with other failure checks in this function if
register_shrinker() failed.

Fixes: d4f59607154b ("vmscan: per-node deferred work")
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: Jan Kara <jack@suse.com>
Cc: Michal Hocko <mhocko@suse.com>
Reviewed-by: Michal Hocko <mhocko@suse.com>
Signed-off-by: Jan Kara <jack@suse.cz>