btrfs: unify checking of IS_ERR and null

use IS_ERR_OR_NULL when possible, done by this coccinelle script:

@ match @
identifier id;
@@
(
- BUG_ON(IS_ERR(id) || !id);
+ BUG_ON(IS_ERR_OR_NULL(id));
|
- IS_ERR(id) || !id
+ IS_ERR_OR_NULL(id)
|
- !id || IS_ERR(id)
+ IS_ERR_OR_NULL(id)
)

Signed-off-by: David Sterba <dsterba@suse.cz>

fs/btrfs/acl.c

@@ -287,7 +287,7 @@ int btrfs_acl_chmod(struct inode *inode)
 		return 0;
 
 	acl = btrfs_get_acl(inode, ACL_TYPE_ACCESS);
-	if (IS_ERR(acl) || !acl)
+	if (IS_ERR_OR_NULL(acl))
 		return PTR_ERR(acl);
 
 	clone = posix_acl_clone(acl, GFP_KERNEL);