drm/radeon/kms: add workaround for dce3 ddc line vbios bug

fixes:
https://bugzilla.kernel.org/show_bug.cgi?id=23752



Signed-off-by: Alex Deucher <alexdeucher@gmail.com>
Cc:stable@kernel.org
Signed-off-by: Dave Airlie <airlied@redhat.com>