FROMLIST: binder: remove dead code in binder_get_ref_for_node

(from https://patchwork.kernel.org/patch/9817819/

)

node is always non-NULL in binder_get_ref_for_node so the
conditional and else clause are not needed

Change-Id: I89ca8c3c0a1a263624a0bd5ddb14e9093ae12009
Signed-off-by: Todd Kjos <tkjos@google.com>