drm/i915: Unify error handling for missing DDI buf trans tables

Handle missing buf trans tables, or out of bounds buf trans levels
the same way everywhere. These should never be hit under normal
conditions, but let's play it safe for now.

v2: Avoid the hdmi_level=-1 case (James)

Cc: James Ausmus <james.ausmus@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171018181934.4229-1-ville.syrjala@linux.intel.com


Reviewed-by: James Ausmus <james.ausmus@intel.com>