drm/i915: adjusted_mode->clock in the dp mode_fixup

... instead of changing mode->clock, which we should leave as-is.

After the previous patch we only touch that if it's a panel, and then
adjusted mode->clock equals adjusted_mode->clock. Outside of
intel_dp.c we only use ajusted_mode->clock in the mode_set functions.

Within intel_dp.c we only use it to calculate the dp dithering
and link bw parameters, so that's the only thing we need to fix
up.

As a temporary ugliness (until the cleanup in the next patch) we
pass the adjusted_mode into dp_dither for both parameters (because
that one still looks at mode->clock).

Note that we do overwrite adjusted_mode->clock with the selected dp
link clock, but that only happens after we've calculated everything we
need based on the dotclock of the adjusted output configuration.

Outside of intel_dp.c only intel_display.c uses adjusted_mode->clock,
and that stays the same after this patch (still equals the selected dp
link clock). intel_display.c also needs the actual dotclock (as
target_clock), but that has been fixed up in the previous patch.

v2: Adjust the debug message to also use adjusted_mode->clock.

Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>