framebuffer compat_ioctl deadlock

Fix deadlock in fb_compat_ioctl.  fb_compat_ioctl acquires a mutex and
calls fb_ioctl that tries to acquire that mutex too.  A regression added
during BKL removal.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>