RDMA/hfi1: Delete unreachable code

All callers allocate MAD structures with proper sizes, there is no need to
recheck it.

Link: https://lore.kernel.org/r/20191029062745.7932-8-leon@kernel.org


Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>