KVM: arm64: Make vcpu const in vcpu_read_sys_reg

vcpu_read_sys_reg should not be modifying the VCPU structure.
Eventually, to handle EL2 sysregs for nested virtualization, we will
call vcpu_read_sys_reg from places that have a const vcpu pointer, which
will complain about the lack of the const modifier on the read path.

Signed-off-by: Christoffer Dall <christoffer.dall@arm.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>

arch/arm64/kvm/sys_regs.c

@@ -76,7 +76,7 @@ static bool write_to_read_only(struct kvm_vcpu *vcpu,
 	return false;
 }
 
-u64 vcpu_read_sys_reg(struct kvm_vcpu *vcpu, int reg)
+u64 vcpu_read_sys_reg(const struct kvm_vcpu *vcpu, int reg)
 {
 	if (!vcpu->arch.sysregs_loaded_on_cpu)
 		goto immediate_read;