KVM: PPC: Book3S HV: smb->smp comment fixup

I made the same typo when trying to grep for uses of smp_wmb and figured
I might as well fix it.
Signed-off-by: NPalmer Dabbelt <palmer@sifive.com>
Signed-off-by: NPaul Mackerras <paulus@ozlabs.org>

arch/powerpc/kvm/book3s_hv.c

@@ -749,7 +749,7 @@ static bool kvmppc_doorbell_pending(struct kvm_vcpu *vcpu)
 	/*
 	 * Ensure that the read of vcore->dpdes comes after the read
 	 * of vcpu->doorbell_request.  This barrier matches the
-	 * smb_wmb() in kvmppc_guest_entry_inject().
+	 * smp_wmb() in kvmppc_guest_entry_inject().
 	 */
 	smp_rmb();
 	vc = vcpu->arch.vcore;