target-s390: Tidy unconditional BRCL

Yes, we're about to rewrite all of this, but having this unconditional
jump recompute cc_op is a large source of "false diff errors" when
trying to examine before and after dumps.

Signed-off-by: Richard Henderson <rth@twiddle.net>

target-s390x/translate.c

diff --git a/target-s390x/translate.c b/target-s390x/translate.c
index 79ab3e5..b8f2ca8 100644
--- a/target-s390x/translate.c
+++ b/target-s390x/translate.c
@@ -3706,6 +3706,11 @@
         tcg_temp_free_i64(tmp);
         break;
     case 0x4: /* BRCL     M1,I2     [RIL] */
+        if (r1 == 15) { /* m1 == r1 */
+            gen_goto_tb(s, 0, target);
+            s->is_jmp = DISAS_TB_JUMP;
+            break;
+        }
         /* m1 & (1 << (3 - cc)) */
         tmp32_1 = tcg_const_i32(3);
         tmp32_2 = tcg_const_i32(1);