RDMA/rxe: Fix comments about removed tasklets

RDMA/rxe: Fix comments about removed tasklets

The commit 9b4b7c1f9f54 ("RDMA/rxe: Add workqueue support for rxe tasks")
removed tasklets and replaced them with a workqueue, but relevant comments
are still remaining in the source code.

Fixes: 9b4b7c1f9f54 ("RDMA/rxe: Add workqueue support for rxe tasks")
Link: https://lore.kernel.org/r/20230518070027.942715-1-matsuda-daisuke@fujitsu.com
Signed-off-by: Daisuke Matsuda <matsuda-daisuke@fujitsu.com>
Reviewed-by: Bob Pearson <rpearsonhpe@gmail.com>
Acked-by: Zhu Yanjun <zyjzyj2000@gmail.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>