KVM: VMX: Add AX to list of registers clobbered by guest switch

By chance this caused no harm so far. We overwrite AX during switch
to/from guest context, so we must declare this.
Signed-off-by: NJan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: NAvi Kivity <avi@redhat.com>

arch/x86/kvm/vmx.c

@@ -4007,7 +4007,7 @@ static void vmx_vcpu_run(struct kvm_vcpu *vcpu)
 #endif
 		[cr2]"i"(offsetof(struct vcpu_vmx, vcpu.arch.cr2))
 	      : "cc", "memory"
-		, R"bx", R"di", R"si"
+		, R"ax", R"bx", R"di", R"si"
 #ifdef CONFIG_X86_64
 		, "r8", "r9", "r10", "r11", "r12", "r13", "r14", "r15"
 #endif