include/linux/fs.h: convert FMODE_* constants to hex

It was tolerable until Eric went and added 8388608.

Cc: Eric Paris <eparis@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>