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

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: 6d868b536f2d (drm/i915: Add WA for planes ending close to left screen edge)
Reviewed-by: Imre Deak <imre.deak@intel.com>
(cherry picked from commit b1f1c2c11fc6c6cd3e361061e30f9b2839897b28)
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>