xfs: fix memory leak in xfs_dir2_node_removename

Fix the leak of kernel memory in xfs_dir2_node_removename()
when xfs_dir2_leafn_remove() returns an error code.

Signed-off-by: Mark Tinguely <tinguely@sgi.com>
Reviewed-by: Ben Myers <bpm@sgi.com>
Signed-off-by: Ben Myers <bpm@sgi.com>