target/riscv/vector_helper.c: fix 'vmvr_v' memcpy endianess

target/riscv/vector_helper.c: fix 'vmvr_v' memcpy endianess

vmvr_v isn't handling the case where the host might be big endian and
the bytes to be copied aren't sequential.

Suggested-by: Richard Henderson <richard.henderson@linaro.org>
Fixes: f714361ed7 ("target/riscv: rvv-1.0: implement vstart CSR")
Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: LIU Zhiwei <zhiwei_liu@linux.alibaba.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-ID: <20240314175704.478276-4-dbarboza@ventanamicro.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>