KVM: x86: don't forget vcpu_put() in kvm_arch_vcpu_ioctl_set_sregs()

Due to a bad merge resolution between commit f298103 ("KVM/x86:
Check input paging mode when cs.l is set") and commit b4ef9d4
("KVM: Move vcpu_load to arch-specific kvm_arch_vcpu_ioctl_set_sregs"),
there is a case in kvm_arch_vcpu_ioctl_set_sregs() where vcpu_put() is
not called after vcpu_get().  Fix it.

Reported-by: syzbot <syzkaller@googlegroups.com>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>

arch/x86/kvm/x86.c

@@ -7706,7 +7706,7 @@ int kvm_arch_vcpu_ioctl_set_sregs(struct kvm_vcpu *vcpu,
 		goto out;
 
 	if (kvm_valid_sregs(vcpu, sregs))
-		return -EINVAL;
+		goto out;
 
 	apic_base_msr.data = sregs->apic_base;
 	apic_base_msr.host_initiated = true;