MAINTAINERS: Fix Soft RoCE location

The Soft RoCE (rxe) is located in drivers/inifiniband/sw
and not in drivers/infiniband/hw/.

This patch fixes it.

Fixes: 8700e3e7 ("Soft RoCE driver")
Signed-off-by: Leon Romanovsky <leon@kernel.org>
Signed-off-by: Doug Ledford <dledford@redhat.com>