xfs: Clean up xfs_attr_node_addname_clear_incomplete

We can use the helper function xfs_attr_node_remove_name to reduce
duplicate code in this function

Signed-off-by: Allison Henderson <allison.henderson@oracle.com>
Reviewed-by: Chandan Babu R <chandanrlinux@gmail.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>