asn1/Makefile.nmake: packet-c1222.c not autogenerated using Windows nmake

Change-Id: I21628bdd1a08348629350a373f1c20e02c3618f7
Reviewed-on: https://code.wireshark.org/review/6007
Reviewed-by: Bill Meier <wmeier@newsguy.com>
(cherry picked from commit 17582d345da954b5b4c8ed2b561dc279cf364562)
Reviewed-on: https://code.wireshark.org/review/6009