i915g: Add missing break statement in i915_debug_packet.

src/gallium/drivers/i915simple/i915_debug.c

@@ -851,6 +851,7 @@ static boolean i915_debug_packet( struct debug_stream *stream )
       default:
 	 return debug(stream, "", 0);
       }
+      break;
    default:
       assert(0);
       return 0;