KVM: x86/mmu: Invert RET_PF_* check when falling through to emulation

Explicitly check for RET_PF_EMULATE instead of implicitly doing the same
by checking for !RET_PF_RETRY (RET_PF_INVALID is handled earlier).  This
will adding new RET_PF_ types in future patches without breaking the
emulation path.

No functional change intended.

Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Message-Id: <20200923220425.18402-3-sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/mmu/mmu.c

@@ -5466,10 +5466,10 @@ int kvm_mmu_page_fault(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa, u64 error_code,
 			return -EIO;
 	}
 
-	if (r == RET_PF_RETRY)
-		return 1;
 	if (r < 0)
 		return r;
+	if (r != RET_PF_EMULATE)
+		return 1;
 
 	/*
 	 * Before emulating the instruction, check if the error code