kvm: x86: Check kvm_write_guest return value in kvm_write_wall_clock

This makes sure the wall clock is updated only after an odd version value
is successfully written to guest memory.

Signed-off-by: Nicholas Krause <xerofoify@gmail.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/x86.c

@@ -1169,7 +1169,8 @@ static void kvm_write_wall_clock(struct kvm *kvm, gpa_t wall_clock)
 
 	++version;
 
-	kvm_write_guest(kvm, wall_clock, &version, sizeof(version));
+	if (kvm_write_guest(kvm, wall_clock, &version, sizeof(version)))
+		return;
 
 	/*
 	 * The guest calculates current wall clock time by adding