compat32: ignore the LOOP_CLR_FD ioctl

compat32: Ignore the LOOP_CLR_FD ioctl for the loop block device, to kill an
annoying kernel message when e.g. busybox umount is used.

Signed-off-by: Geert Uytterhoeven <Geert.Uytterhoeven@sonycom.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>