vfio/type1: remove hugepage checks in is_invalid_reserved_pfn()

Currently, no hugepage split code can transfer the reserved bit
from head to tail during the split, so checking the head can't make
a difference in a racing condition with hugepage spliting.

The buddy wouldn't allow a driver to allocate an hugepage if any
subpage is reserved in the e820 map at boot, if any driver sets the
reserved bit of head page before mapping the hugepage in userland,
it needs to set the reserved bit in all subpages to be safe.

Signed-off-by: Ben Luo <luoben@linux.alibaba.com>
Reviewed-by: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>