drm/i915: Remove unnecessary test on the gen in intel_do_mmio_flip()

use_mmio_flip() makes sure we only enable MMIO flips on gen5+. So we
don't need to take into account older devices.
Signed-off-by: Damien Lespiau <damien.lespiau@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_display.c

@@ -9567,12 +9567,11 @@ static void intel_do_mmio_flip(struct intel_crtc *intel_crtc)
 	reg = DSPCNTR(intel_crtc->plane);
 	dspcntr = I915_READ(reg);
 
-	if (INTEL_INFO(dev)->gen >= 4) {
 	if (obj->tiling_mode != I915_TILING_NONE)
 		dspcntr |= DISPPLANE_TILED;
 	else
 		dspcntr &= ~DISPPLANE_TILED;
-	}
+
 	I915_WRITE(reg, dspcntr);
 
 	I915_WRITE(DSPSURF(intel_crtc->plane),