drm/i915: Restore correct bxt_ddi_phy_calc_lane_lat_optim_mask() calculation

We are no longer calling bxt_ddi_phy_calc_lane_lat_optim_mask() when
intel{hdmi,dp}_compute_config() succeeds, and instead only call it
when those fail. This is fallout from the bool->int
.compute_config() conversion which failed to invert the return
value check before calling bxt_ddi_phy_calc_lane_lat_optim_mask().
Let's just replace it with an early bailout so that it's harder
to miss.

This restores the correct latency optim setting calculation
(which could fix some real failures), and avoids the
MISSING_CASE() from bxt_ddi_phy_calc_lane_lat_optim_mask()
after intel{hdmi,dp}_compute_config() has failed.

Cc: Lyude Paul <lyude@redhat.com>
Fixes: 204474a6

 ("drm/i915: Pass down rc in intel_encoder->compute_config()")
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=109373
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190411164925.28491-1-ville.syrjala@linux.intel.com
Reviewed-by: Lyude Paul <lyude@redhat.com>
(cherry picked from commit 7a412b8f

)
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>