The open function got the BKL via the big push down. Replace it by
preempt_enable/disable as this is sufficient for an UP machine.

The ioctl can be unlocked because there is no functionality which
requires serialization. The usage by multiple callers is broken with
and without the BKL due to the local static variable addr.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>