drm/i915/pch: Cosmetic fix to FDI link training

Unmask the bits for link training reporting before starting link
training.  If stage 1 training finished before we unmask them, then we'd
spin around in a loop a few times until smashing on through.  Which is
harmless, since training _did_ succeed, it just looks ugly in dmesg.

Signed-off-by: Adam Jackson <ajax@redhat.com>
Signed-off-by: Eric Anholt <eric@anholt.net>