mf: Fix several reference leaks.
So that the mf tests pass again on 32bit on the testbot, though they still fail locally with LIBGL_ALWAYS_SOFTWARE=true GALLIUM_DRIVER=softpipe.
So that the mf tests pass again on 32bit on the testbot, though they still fail locally with LIBGL_ALWAYS_SOFTWARE=true GALLIUM_DRIVER=softpipe.