devel/pkgconf: fix regression introduced by last minute patch

the last minute patch was intended to fix a bug in pkgconf which broke
the expected behaviour of cabal (haskell)

$ pkgconf --modversion atf-c atf-c++
0.21
0.21
0.21

due to bad pattern matching, the fix was a bit too harsh and broke the
version comparison
$ pkgconf --modversion "gtk+-2.0 >= 2.0.0"

Reported by: cmt