RDMA/mlx5: Set mkeys for dmabuf at PAGE_SIZE

RDMA/mlx5: Set mkeys for dmabuf at PAGE_SIZE

Set the mkey for dmabuf at PAGE_SIZE to support any SGL
after a move operation.

ib_umem_find_best_pgsz returns 0 on error, so it is
incorrect to check the returned page_size against PAGE_SIZE

Fixes: 90da7dc8206a ("RDMA/mlx5: Support dma-buf based userspace memory region")
Signed-off-by: Chiara Meiohas <cmeiohas@nvidia.com>
Reviewed-by: Michael Guralnik <michaelgur@nvidia.com>
Link: https://lore.kernel.org/r/1e2289b9133e89f273a4e68d459057d032cbc2ce.1718301631.git.leon@kernel.org
Signed-off-by: Leon Romanovsky <leon@kernel.org>