RDMA/erdma: Use fixed hardware page size

Hardware's page size is 4096, but the kernel's page size may vary. Driver
should use hardware's page size when communicating with hardware.

Fixes: 15505577 ("RDMA/erdma: Add verbs implementation")
Link: https://lore.kernel.org/r/20230307102924.70577-2-chengyou@linux.alibaba.com


Signed-off-by: Cheng Xu <chengyou@linux.alibaba.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>