The function ib_modify_wq() is not used, so remove it.

Link: https://lore.kernel.org/r/c5e48d517b9163fe4f9ffd224050b83fdb3571c6.1620552935.git.leonro@nvidia.comSigned-off-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>