target/riscv: pmp: remove redundant check in pmp_is_locked

target/riscv: pmp: remove redundant check in pmp_is_locked

Remove useless check in pmp_is_locked, the function will return 0 in either
case.

Signed-off-by: Loïc Lefort <loic@rivosinc.com>
Reviewed-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: LIU Zhiwei <zhiwei_liu@linux.alibaba.com>
Message-ID: <20250313193011.720075-6-loic@rivosinc.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>