target/riscv: rvv-1.0: fix address index overflow bug of indexed load/store insns

target/riscv: rvv-1.0: fix address index overflow bug of indexed load/store insns

Replace ETYPE from signed int to unsigned int to prevent index overflow
issue, which would lead to wrong index address.

Signed-off-by: Frank Chang <frank.chang@sifive.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-Id: <20211210075704.23951-23-frank.chang@sifive.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>