mm/page_owner.c: use PTR_ERR_OR_ZERO()

Fix ptr_ret.cocci warnings:

  mm/page_owner.c:639:1-3: WARNING: PTR_ERR_OR_ZERO can be used

Use PTR_ERR_OR_ZERO rather than if(IS_ERR(...)) + PTR_ERR

Generated by: scripts/coccinelle/api/ptr_ret.cocci

Link: http://lkml.kernel.org/r/1511824101-9597-1-git-send-email-gomonovych@gmail.com
Signed-off-by: Vasyl Gomonovych <gomonovych@gmail.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Michal Hocko <mhocko@suse.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/page_owner.c

@@ -635,9 +635,7 @@ static int __init pageowner_init(void)
 
 	dentry = debugfs_create_file("page_owner", S_IRUSR, NULL,
 			NULL, &proc_page_owner_operations);
-	if (IS_ERR(dentry))
-		return PTR_ERR(dentry);
 
-	return 0;
+	return PTR_ERR_OR_ZERO(dentry);
 }
 late_initcall(pageowner_init)