fanotify: only destroy a mark if both its mask and its ignored_mask are cleared

Currently we destroy a mark if one of its masks - event mask or ignored mask - are
cleared without checking if the other mask is also clear.

With this patch we only destroy a mark if both masks are cleared.

Signed-off-by: Lino Sanfilippo <LinoSanfilippo@gmx.de>
Signed-off-by: Eric Paris <eparis@redhat.com>