IB/hfi1: Handle kzalloc failure in init_pervl_scs

Checking the return value of the memory allocation call in
init_pervl_scs() was missed.  Recently the kmalloc() was changed to
kzalloc() which identified the problem.

While fixing this issue 2 other bugs were noticed.  First, the array
being allocated is accessed in the nomem path which can be reached before
it is allocated.  Second, kernel_send_context was not released on error.
Fix both of these by creating a more common memory unwind label structure.

Fixes: 35f6befc ("staging/rdma/hfi1: Add qp to send context mapping for PIO")
Reported-by: Leon Romanovsky <leon@kernel.org>
Reviewed-by: Mike Marciniszyn <mike.marciniszyn@intel.com>
Signed-off-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
Signed-off-by: Ira Weiny <ira.weiny@intel.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>