RDMA/mlx5: Remove duplicated assignment to variable rcqe_sz

RDMA/mlx5: Remove duplicated assignment to variable rcqe_sz

The variable rcqe_sz is being unnecessarily assigned twice, fix this by
removing one of the duplicates.

Fixes: 8bde2c509e40 ("RDMA/mlx5: Update all DRIVER QP places to use QP subtype")
Link: https://lore.kernel.org/r/20200507151610.52636-1-colin.king@canonical.com
Addresses-Coverity: ("Evaluation order violation")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Acked-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>