xen: mapcache: Fix unmapping of first entries in buckets
This fixes the clobbering of the entry->next pointer when
unmapping the first entry in a bucket of a mapcache.
Fixes: 123acd816d ("xen: mapcache: Unmap first entries in buckets") Reported-by: Anthony PERARD <anthony.perard@vates.tech> Signed-off-by: Edgar E. Iglesias <edgar.iglesias@amd.com> Reviewed-by: Anthony PERARD <anthony.perard@vates.tech> Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>