staging: wfx: drop useless union hif_event_data

The union hif_event_data is never used in the driver. So, it is
not necessary to declare it separately from hif_ind_event.

Signed-off-by: Jérôme Pouiller <jerome.pouiller@silabs.com>
Link: https://lore.kernel.org/r/20200907101521.66082-24-Jerome.Pouiller@silabs.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>