Staging: agnx: fix build errors due to rate control API changes

In commit e6a9854b

, the rate control API
was rewritten, so make the needed changes to the agnx driver so that it
will build and work properly.

Cc: Li YanBo <dreamfly281@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>