target/riscv: Factor MemOp variable out when MO_TE is set

target/riscv: Factor MemOp variable out when MO_TE is set

In preparation of automatically replacing the MO_TE flag
in the next commit, use an local @memop variable.

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-ID: <20251010155045.78220-12-philmd@linaro.org>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>