GPRSCDR: fix warning: 'dissect_gprscdr_MBMSInformation' defined but not use

Change-Id: I4bdbaeb3c1e3327af6f5e3de22ebcd4472b9f3e7
Reviewed-on: https://code.wireshark.org/review/5706
Reviewed-by: Anders Broman <a.broman58@gmail.com>