physmem: Bail out qemu_ram_block_from_host() for invalid ram addrs

Bail out in qemu_ram_block_from_host() when
xen_ram_addr_from_mapcache() does not find an existing
mapping.

Signed-off-by: Edgar E. Iglesias <edgar.iglesias@amd.com>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>
1 file changed