target/riscv: rvv: Fix incorrect vlen comparison in prop_vlen_set

target/riscv: rvv: Fix incorrect vlen comparison in prop_vlen_set

In prop_vlen_set function, there is an incorrect comparison between
vlen(bit) and vlenb(byte).
This will cause unexpected error when user applies the `vlen=1024` cpu
option with a vendor predefined cpu type that the default vlen is
1024(vlenb=128).

Fixes: 4f6d036ccc ("target/riscv/cpu.c: remove cpu->cfg.vlen")
Signed-off-by: Max Chou <max.chou@sifive.com>
Reviewed-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Message-ID: <20250124090539.2506448-1-max.chou@sifive.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>
(cherry picked from commit bf3adf93f16730ca5aaa6c26cf969e64eeff6e7b)
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>