drm/i915: Replace "INTEL_INFO->gen == x" checks with IS_GENx

This way optimization from a previous patch works even better.

v2: Rebase.

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
diff --git a/drivers/gpu/drm/i915/intel_lvds.c b/drivers/gpu/drm/i915/intel_lvds.c
index bc53c0d..d65fd94 100644
--- a/drivers/gpu/drm/i915/intel_lvds.c
+++ b/drivers/gpu/drm/i915/intel_lvds.c
@@ -190,7 +190,7 @@
 	/* Set the dithering flag on LVDS as needed, note that there is no
 	 * special lvds dither control bit on pch-split platforms, dithering is
 	 * only controlled through the PIPECONF reg. */
-	if (INTEL_INFO(dev)->gen == 4) {
+	if (IS_GEN4(dev_priv)) {
 		/* Bspec wording suggests that LVDS port dithering only exists
 		 * for 18bpp panels. */
 		if (crtc->config->dither && crtc->config->pipe_bpp == 18)