LoongArch: KVM: Fix max supported vCPUs set with EIOINTC

LoongArch: KVM: Fix max supported vCPUs set with EIOINTC

VM fails to boot with 256 vCPUs, the detailed command is

  qemu-system-loongarch64 -smp 256

and there is an error reported as follows:

  KVM_LOONGARCH_EXTIOI_INIT_NUM_CPU failed: Invalid argument

There is typo issue in function kvm_eiointc_ctrl_access() when set
max supported vCPUs.

Cc: stable@vger.kernel.org
Fixes: 47256c4c8b1b ("LoongArch: KVM: Avoid copy_*_user() with lock hold in kvm_eiointc_ctrl_access()")
Signed-off-by: Bibo Mao <maobibo@loongson.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>