target-s390x: Fix wrong argument in call of tcg_gen_shl_i64()

tcg_gen_shl_i64 needs a 3rd argument of type TCGv_i64.
Set tmp4 so it can be used here.

v2:
Don't call tcg_const_i64() inside of the loop
because it creates additional code.

Signed-off-by: Stefan Weil <weil@mail.berlios.de>
Signed-off-by: Alexander Graf <agraf@suse.de>
