kill-the-bkl/reiserfs: definitely drop the bkl from reiserfs_ioctl()

The reiserfs ioctl path doesn't need the big kernel lock anymore , now
that the filesystem synchronizes through its own lock.

We can then turn reiserfs_ioctl() into an unlocked_ioctl callback.

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Jeff Mahoney <jeffm@suse.com>
Cc: Chris Mason <chris.mason@oracle.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Alexander Beregalov <a.beregalov@gmail.com>
Cc: Laurent Riffard <laurent.riffard@free.fr>
Cc: Thomas Gleixner <tglx@linutronix.de>