GFS2: Use an IS_ERR test rather than a NULL test

In case of error, the function gfs2_inode_lookup returns an
ERR pointer, but never returns a NULL pointer. So a NULL test that
necessarily comes after an IS_ERR test should be deleted, and a NULL
test that may come after a call to this function should be
strengthened by an IS_ERR test.

The semantic match that finds this problem is as follows:
(http://www.emn.fr/x-info/coccinelle/)

// <smpl>
@match_bad_null_test@
expression x, E;
statement S1,S2;
@@
x = gfs2_inode_lookup(...)
... when != x = E
* if (x != NULL)
S1 else S2
// </smpl>

Signed-off-by:  Julien Brunel <brunel@diku.dk>
Signed-off-by:  Julia Lawall <julia@diku.dk>
Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>

fs/gfs2/inode.c

@@ -1033,13 +1033,11 @@ struct inode *gfs2_createi(struct gfs2_holder *ghs, const struct qstr *name,
 
 	if (bh)
 		brelse(bh);
-	if (!inode)
-		return ERR_PTR(-ENOMEM);
 	return inode;
 
 fail_gunlock2:
 	gfs2_glock_dq_uninit(ghs + 1);
-	if (inode)
+	if (inode && !IS_ERR(inode))
 		iput(inode);
 fail_gunlock:
 	gfs2_glock_dq(ghs);