Fix leak in __btrfs_map_block error path

If we bail out when the stripe alloc fails, we need to undo the
earlier allocation of raid_map.

Signed-off-by: Dave Jones <davej@redhat.com>
Signed-off-by: Josef Bacik <jbacik@fusionio.com>
Signed-off-by: Chris Mason <chris.mason@fusionio.com>
diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 93f39b1..44abd15 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -4673,6 +4673,7 @@
 	}
 	bbio = kzalloc(btrfs_bio_size(num_alloc_stripes), GFP_NOFS);
 	if (!bbio) {
+		kfree(raid_map);
 		ret = -ENOMEM;
 		goto out;
 	}