rate_control_rate_init assumes the rate_init member of
struct rate_control_ops is not NULL therefore not initializing it leads to
an oops as soon the driver succesfully associates to an AP.
Signed-off-by: Catalin Iacob <iacobcatalin@gmail.com> Acked-by: Larry Finger <Larry.Finger@lwfinger.net> Signed-off-by: John W. Linville <linville@tuxdriver.com>