bnxt_re: fix the regression due to changes in alloc_pbl

While adding the use of for_each_sg_dma_page iterator for Brodcom's rdma
driver, there was a regression added in the __alloc_pbl path. The change
left bnxt_re in DOA state in for-next branch.

Fixing the regression to avoid the host crash when a user space object is
created. Restricting the unconditional access to hwq.pg_arr when hwq is
initialized for user space objects.

Fixes: 161ebe24 ("RDMA/bnxt_re: Use for_each_sg_dma_page iterator on umem SGL")
Reported-by: Gal Pressman <galpress@amazon.com>
Signed-off-by: Selvin Xavier <selvin.xavier@broadcom.com>
Signed-off-by: Devesh Sharma <devesh.sharma@broadcom.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>