ARM: kvm: replace open coded VA->PA calculations with adr_l call

commit aaac3733 upstream.

Replace the open coded calculations of the actual physical address
of the KVM stub vector table with a single adr_l invocation.

Reviewed-by: Nicolas Pitre <nico@fluxnic.net>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>