btrfs: return block group directly at btrfs_next_block_group()

At btrfs_next_block_group(), we have this long line with two statements:

  cache = btrfs_lookup_first_block_group(...); return cache;

This makes it a bit harder to read due to two statements on the same
line, so change that to directly return the result of the call to
btrfs_lookup_first_block_group().
Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/block-group.c

@@ -271,7 +271,7 @@ struct btrfs_block_group *btrfs_next_block_group(
 
 		read_unlock(&fs_info->block_group_cache_lock);
 		btrfs_put_block_group(cache);
-		cache = btrfs_lookup_first_block_group(fs_info, next_bytenr); return cache;
+		return btrfs_lookup_first_block_group(fs_info, next_bytenr);
 	}
 	node = rb_next(&cache->cache_node);
 	btrfs_put_block_group(cache);