Instead of overwriting QP init attributes with driver QP subtype,
use that subtype directly. This change will allow us to remove
logic which cached QP init attributes.

Link: https://lore.kernel.org/r/20200427154636.381474-10-leon@kernel.orgReviewed-by: NMaor Gottlieb <maorg@mellanox.com>
Signed-off-by: NLeon Romanovsky <leonro@mellanox.com>
Signed-off-by: NJason Gunthorpe <jgg@mellanox.com>