btrfs: merge setting ret and return ret

In many places we have pattern:

	ret = ...;
	return ret;

This can be simplified to a direct return, removing 'ret' if not
otherwise needed. The places in self tests are not converted so we can
add more test cases without changing surrounding code
(extent-map-tests.c:test_case_4()).

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

fs/btrfs/file.c

@@ -1272,8 +1272,7 @@ again:
 		btrfs_delalloc_release_extents(inode, reserved_len);
 		release_space(inode, *data_reserved, reserved_start, reserved_len,
 			      only_release_metadata);
-		ret = extents_locked;
-		return ret;
+		return extents_locked;
 	}
 
 	copied = copy_folio_from_iter_atomic(folio, offset_in_folio(folio, start),