comms/opencbm-plugin-xa1541: Fix run depends

The XA1541 plugin must depend on the exact same version of opencbm base.

• Make sure both ports use the same PORTREVISION by defining it in comms/opencbm/Makefile.inc and enforcing no explicit definition in the port Makefiles.
• Use PKGVERSION instead of PORTVERSION to construct the dependency.

Reported by: pkg-fallout