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>
diff --git a/fs/btrfs/relocation.c b/fs/btrfs/relocation.c
index 199a801..fed0aae 100644
--- a/fs/btrfs/relocation.c
+++ b/fs/btrfs/relocation.c
@@ -3220,7 +3220,7 @@
 	key.offset = 0;
 
 	inode = btrfs_iget(fs_info->sb, &key, root, NULL);
-	if (!inode || IS_ERR(inode) || is_bad_inode(inode)) {
+	if (IS_ERR_OR_NULL(inode) || is_bad_inode(inode)) {
 		if (inode && !IS_ERR(inode))
 			iput(inode);
 		return -ENOENT;