staging: wfx: simplify wfx_update_filtering()

Inline wfx_set_mcast_filter() into wfx_update_filtering() and remove
useless intermediate variables.

Signed-off-by: Jérôme Pouiller <jerome.pouiller@silabs.com>
Link: https://lore.kernel.org/r/20200415161147.69738-3-Jerome.Pouiller@silabs.com


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