mmtimer: Push BKL down into the ioctl handler

Switches to unlocked_ioctl read to remove ioctl BKL method. Fix the
unknown ioctl return. Probably a nice easy one to kill off BKL usage
entirely later

Signed-off-by: Alan Cox <alan@redhat.com>
Acked-by: Jes Sorensen <jes@sgi.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>