target: Use if/else for sa_res_key conditional in emulate_pro_register()

Don't need goto, we can just do an if/else for sa_res_key behavior. Move
shorter case first. Slightly shorter b/c both cases can share a call to
update_and_write_aptpl() now.

Signed-off-by: Andy Grover <agrover@redhat.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>