ip27-rtc: convert ioctl to unlocked_ioctl

Convert ioctl call to unlocked_ioctl form.  It is possible (in that simple
way) due to a spinlock protection.

Signed-off-by: Cyrill Gorcunov <gorcunov@gmail.com>
Acked-by: Jiri Slaby <jirislaby@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>