Mk/Uses: Fix feature checks after my previous {WITH,WITHOUT}_*_PORTS change

[arrowd]

Test Plan

Take cmake.mk for example. Choosing a port with USES=cmake and running make -V CMAKE_BUILD_TYPE gives "Release" and make -V CMAKE_BUILD_TYPE WITH_DEBUG=yes gives "Debug". However, make -V CMAKE_BUILD_TYPE WITH_DEBUG_PORTS=this/port still gives "Release" without this change.