RDMA/mlx4: remove redundant assignment to variable nreq

Variable nreq is being assigned a value that is never read. The assignment
is redundant and can be removed.

Link: https://lore.kernel.org/r/20220130225747.8114-1-colin.i.king@gmail.com


Signed-off-by: Colin Ian King <colin.i.king@gmail.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>