RDMA/umem: remove FOLL_FORCE usage

GUP now supports reliable R/O long-term pinning in COW mappings, such
that we break COW early. MAP_SHARED VMAs only use the shared zeropage so
far in one corner case (DAXFS file with holes), which can be ignored
because GUP does not support long-term pinning in fsdax (see
check_vma_flags()).

Consequently, FOLL_FORCE | FOLL_WRITE | FOLL_LONGTERM is no longer required
for reliable R/O long-term pinning: FOLL_LONGTERM is sufficient. So stop
using FOLL_FORCE, which is really only for ptrace access.

Link: https://lkml.kernel.org/r/20221116102659.70287-11-david@redhat.com


Tested-by: Leon Romanovsky <leonro@nvidia.com>	[over mlx4 and mlx5]
Signed-off-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Cc: Leon Romanovsky <leon@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>