fsnotify: initialize mask in fsnotify_perm

akpm got a warning the fsnotify_mask could be used uninitialized in
fsnotify_perm().  It's not actually possible but his compiler complained
about it.  This patch just initializes it to 0 to shut up the compiler.

Reported-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Eric Paris <eparis@redhat.com>