GFS2: Fix permissions checking for setflags ioctl()

commit 7df0e039 upstream.

We should be checking for the ownership of the file for which
flags are being set, rather than just for write access.

Reported-by: Dan Rosenberg <dan.j.rosenberg@gmail.com>
Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>