drm/i915: Add a default case in gen7 hwsp switch-case

Gen7 won't get any new engines, and we already added VCS2 there to just
silence gcc's not handled in switch warnings.

Use a default case instead, otherwise we will need to keep adding extra
cases if changes happen in the future.

v2: Since reaching the default case is impossible, use GEM_BUG_ON (Chris).

Cc: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Michel Thierry <michel.thierry@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20170830180115.907-1-michel.thierry@intel.comReviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

drivers/gpu/drm/i915/intel_ringbuffer.c

@@ -402,17 +402,18 @@ static void intel_ring_setup_status_page(struct intel_engine_cs *engine)
 	 */
 	if (IS_GEN7(dev_priv)) {
 		switch (engine->id) {
+		/*
+		 * No more rings exist on Gen7. Default case is only to shut up
+		 * gcc switch check warning.
+		 */
+		default:
+			GEM_BUG_ON(engine->id);
 		case RCS:
 			mmio = RENDER_HWS_PGA_GEN7;
 			break;
 		case BCS:
 			mmio = BLT_HWS_PGA_GEN7;
 			break;
-		/*
-		 * VCS2 actually doesn't exist on Gen7. Only shut up
-		 * gcc switch check warning
-		 */
-		case VCS2:
 		case VCS:
 			mmio = BSD_HWS_PGA_GEN7;
 			break;