target/ppc: Fix temp usage in gen_op_arith_modw

Fix a crash writing to 't3', which is now a constant.
Instead, write the result of the remu to 't1'.

Fixes: 7058ff52 ("target/ppc: Avoid tcg_const_* in translate.c")
Reported-by: Nicholas Piggin <npiggin@gmail.com>
Reviewed-by: Anton Johansson <anjo@rev.ng>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Cédric Le Goater <clg@kaod.org>