RDMA/ocrdma: Use ib_umem_num_dma_blocks() instead of ib_umem_page_count()

This driver always uses a DMA array made up of PAGE_SIZE elements, so just
use ib_umem_num_dma_blocks().

Since rdma_for_each_dma_block() always iterates exactly
ib_umem_num_dma_blocks() there is no need for the early exit check in
build_user_pbes(), delete it.

Link: https://lore.kernel.org/r/13-v2-270386b7e60b+28f4-umem_1_jgg@nvidia.com


Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>