drm/i915: gen 9 h/w w/a Fix stepping check

Fixed the stepping check on WaDisableDgMirrorFixInHalfSliceChicken5
to be for the correct SOC (Skylake)
Signed-off-by: Nick Hoath <nicholas.hoath@intel.com>
Reviewed-by: Damien Lespiau <damien.lespiau@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_ringbuffer.c

@@ -886,7 +886,8 @@ static int gen9_init_workarounds(struct intel_engine_cs *ring)
 	WA_SET_BIT_MASKED(HALF_SLICE_CHICKEN3,
 			  GEN9_DISABLE_OCL_OOB_SUPPRESS_LOGIC);
 
-	if (INTEL_REVID(dev) == SKL_REVID_A0) {
+	if (INTEL_REVID(dev) >= SKL_REVID_A0 &&
+	    INTEL_REVID(dev) <= SKL_REVID_B0) {
 		/*
 		* WaDisableDgMirrorFixInHalfSliceChicken5:skl
 		* This is a pre-production w/a.