target/rx/translate: Add missing fall through comment

Coverity reported a missing fall through comment, add it.

Fixes: e5918d7 ("target/rx: TCG translation")
Reported-by: Coverity (CID 1422222 MISSING_BREAK)
Suggested-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20200403184419.28556-1-philmd@redhat.com>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

target/rx/translate.c

@@ -2362,6 +2362,7 @@ static void rx_tr_tb_stop(DisasContextBase *dcbase, CPUState *cs)
         break;
     case DISAS_UPDATE:
         tcg_gen_movi_i32(cpu_pc, ctx->base.pc_next);
+        /* fall through */
     case DISAS_EXIT:
         tcg_gen_exit_tb(NULL, 0);
         break;