target/s390x: Fix relative long instructions with large offsets

The expression "imm * 2" in gen_ri2() can wrap around if imm is large
enough.

Fix by casting imm to int64_t, like it's done in disas_jdest().

Fixes: e8ecdfe ("Fix EXECUTE of relative branches")
Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Message-Id: <20230704081506.276055-8-iii@linux.ibm.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>

target/s390x/tcg/translate.c

@@ -5794,7 +5794,7 @@ static TCGv gen_ri2(DisasContext *s)
 
     disas_jdest(s, i2, is_imm, imm, ri2);
     if (is_imm) {
-        ri2 = tcg_constant_i64(s->base.pc_next + imm * 2);
+        ri2 = tcg_constant_i64(s->base.pc_next + (int64_t)imm * 2);
     }
 
     return ri2;