xfs: fix up backport error in fs/xfs/xfs_inode.c

Commit c66edeaf, which was a backport of
commit b1438f47 upstream, needed to have
the error value be positive, not negative, in order to work properly.
Reported-by: "Thomas D." <whissi@whissi.de>
Reported-by: Brad Spender <spender@grsecurity.net>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Willy Tarreau <w@1wt.eu>
Cc: Jiri Slaby <jslaby@suse.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

fs/xfs/xfs_inode.c

@@ -3098,7 +3098,7 @@ xfs_iflush(
 	 */
 	error = xfs_imap_to_bp(mp, NULL, &ip->i_imap, &dip, &bp, XBF_TRYLOCK,
 			       0);
-	if (error == -EAGAIN) {
+	if (error == EAGAIN) {
 		xfs_ifunlock(ip);
 		return error;
 	}