sysfs: checking for NULL instead of ERR_PTR

d_path() returns an ERR_PTR and it doesn't return NULL.
Signed-off-by: Dan Carpenter <error27@gmail.com>
Cc: stable <stable@kernel.org>
Reviewed-by: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

fs/sysfs/file.c

@@ -340,7 +340,7 @@ static int sysfs_open_file(struct inode *inode, struct file *file)
 	char *p;
 
 	p = d_path(&file->f_path, last_sysfs_file, sizeof(last_sysfs_file));
-	if (p)
+	if (!IS_ERR(p))
 		memmove(last_sysfs_file, p, strlen(p) + 1);
 
 	/* need attr_sd for attr and ops, its parent for kobj */