drm/i915: Make HW readout mark CRTC scaler as in use.

This way we don't accidentally double allocate it.
Noticed this when I wrote a patch to sanity check all of
the scaler state.
Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190108160842.13396-4-maarten.lankhorst@linux.intel.com

drivers/gpu/drm/i915/intel_display.c

@@ -8878,6 +8878,7 @@ static void skylake_get_pfit_config(struct intel_crtc *crtc,
 			pipe_config->pch_pfit.enabled = true;
 			pipe_config->pch_pfit.pos = I915_READ(SKL_PS_WIN_POS(crtc->pipe, i));
 			pipe_config->pch_pfit.size = I915_READ(SKL_PS_WIN_SZ(crtc->pipe, i));
+			scaler_state->scalers[i].in_use = true;
 			break;
 		}
 	}