drm/radeon: fix eDP clk and lane setup for scaled modes

commit 93927f9c1db5f55085457e820f0631064c7bfa34 upstream.

Need to use the adjusted mode since we are sending native
timing and using the scaler for non-native modes.

Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Jerome Glisse <jglisse@redhat.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>