drm/i915: Make the report about a bogus stolen reserved area an error

Now that we should be properly filtering out the cases when the stolen
reserved area is disabled, let's convert the debug message about a
misplaced reserved area into an error.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171102151737.23336-2-ville.syrjala@linux.intel.com


Reviewed-by: Paulo Zanoni <paulo.r.zanoni@intel.com>