KVM: SVM: fix up incorrect backport

When I backported 52918ed5fcf0 ("KVM: SVM: Override default MMIO mask if
memory encryption is enabled") to 4.19 (which resulted in commit
a4e761c9 ("KVM: SVM: Override default MMIO mask if memory encryption
is enabled")), I messed up the call to kvm_mmu_set_mmio_spte_mask()

Fix that here now.

Reported-by: Tom Lendacky <thomas.lendacky@amd.com>
Cc: Sean Christopherson <sean.j.christopherson@intel.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>