cmd/compile/internal/ssa: mark opPPC64ADDZE as having a flag input

cmd/compile/internal/ssa: mark opPPC64ADDZE as having a flag input

This was missed in CL 571055.

Change-Id: I58d6469c9ea323943e9c230a54fba8f7ec705d47
Reviewed-on: https://go-review.googlesource.com/c/go/+/573515
Reviewed-by: Than McIntosh <thanm@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Reviewed-by: Lynn Boger <laboger@linux.vnet.ibm.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>