drm/i915: Fix glk/cnl display w/a #1175

The workaround was supposed to look at the plane destination
coordinates. Currently it's looking at some mixture of src
and dst coordinates that doesn't make sense. Fix it up.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180719182214.4323-2-ville.syrjala@linux.intel.com


Fixes: 394676f0 (drm/i915: Add WA for planes ending close to left screen edge)
Reviewed-by: Imre Deak <imre.deak@intel.com>