disas/riscv: Chain "ret" pseudo off "jr" pseudo

"jr" has already checked two conditions that apply to "ret".

Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Message-ID: <20260812223142.349142-31-richard.henderson@linaro.org>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>