cramfs: fix incorrect physical page address calculation

Commit 21aa65bf ("mm: remove callers of pfn_t functionality")
incorrectly replaced the pfn with the physical address when calling
vmf_insert_mixed().  Instead the phys_to_pfn_t() call should have been
replaced with PHYS_PFN().

Found by inspection after a similar issue was noted in fuse virtio_fs.

Link: https://lkml.kernel.org/r/20250923005333.3165032-1-apopple@nvidia.com


Fixes: 21aa65bf ("mm: remove callers of pfn_t functionality")
Signed-off-by: Alistair Popple <apopple@nvidia.com>
Reviewed-by: Dev Jain <dev.jain@arm.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Cc: Haiyue Wang <haiyuewa@163.com>
Cc: Nicolas Pitre <nico@fluxnic.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>