net: devmem: move list_add to net_devmem_bind_dmabuf.

It's annoying for the list_add to be outside net_devmem_bind_dmabuf, but
the list_del is in net_devmem_unbind_dmabuf. Make it consistent by
having both the list_add/del be inside the net_devmem_[un]bind_dmabuf.

Cc: ap420073@gmail.com
Signed-off-by: Mina Almasry <almasrymina@google.com>
Tested-by: Taehee Yoo <ap420073@gmail.com>
Acked-by: Stanislav Fomichev <sdf@fomichev.me>
Link: https://patch.msgid.link/20250523230524.1107879-2-almasrymina@google.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>