Fix debugfs_create_file's error checking method for arch/sh/mm/

debugfs_create_file() returns NULL if an error occurs, returns -ENODEV
when debugfs is not enabled in the kernel.

Signed-off-by: Zhao Lei <zhaolei@cn.fujitsu.com>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>

arch/sh/mm/pmb.c

@@ -394,6 +394,8 @@ static int __init pmb_debugfs_init(void)
 
 	dentry = debugfs_create_file("pmb", S_IFREG | S_IRUGO,
 				     sh_debugfs_root, NULL, &pmb_debugfs_fops);
+	if (!dentry)
+		return -ENOMEM;
 	if (IS_ERR(dentry))
 		return PTR_ERR(dentry);