KVM: nVMX: Explicitly reference the scratch reg in nested early checks

Using %1 to reference RCX, i.e. the 'vmx' pointer', is obtuse and
fragile, e.g. it results in cryptic and infurating compile errors if the
output constraints are touched by anything more than a gentle breeze.
Reviewed-by: Jim Mattson <jmattson@google.com>
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/vmx/nested.c

@@ -2757,7 +2757,7 @@ static int nested_vmx_check_vmentry_hw(struct kvm_vcpu *vcpu)
 		/* Set HOST_RSP */
 		"sub $%c[wordsize], %%" _ASM_SP "\n\t" /* temporarily adjust RSP for CALL */
 		__ex("vmwrite %%" _ASM_SP ", %%" _ASM_DX) "\n\t"
-		"mov %%" _ASM_SP ", %c[host_rsp](%1)\n\t"
+		"mov %%" _ASM_SP ", %c[host_rsp](%% " _ASM_CX ")\n\t"
 		"add $%c[wordsize], %%" _ASM_SP "\n\t" /* un-adjust RSP */
 
 		/* Check if vmlaunch or vmresume is needed */