KVM: mips: use id_to_memslot correctly

commit 69a12200 upstream.

The argument to KVM_GET_DIRTY_LOG is a memslot id; it may not match the
position in the memslots array, which is sorted by gfn.

Reviewed-by: James Hogan <james.hogan@imgtec.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>