Fix LIB_DEPENDS for the DBUS option.

The dependency on devel/dbus was still using a shorthand name instead of the
full file name of the library.

Not bumping PORTREVISION because the build was broken before if the DBUS
option was on.

PR: 198223
Submitted by: Tobias Berner <tcberner@gmail.com>
Approved by: glebius (maintainer)
MFH: 2015Q1