mwifiex: delete unused mwifiex_get_intf_num()

mwifiex: delete unused mwifiex_get_intf_num()

commit bc05287de51f4bd71765afda4215b6cbbce7ed68 upstream.

Commit 69ff26296b09 ("mwifiex: update set_mac_address logic") fixed the
only user of this function, partly because the author seems to have
noticed that, as written, it's on the borderline between highly
misleading and buggy.

Anyway, no sense in keeping dead code around: let's drop it.

Fixes: 69ff26296b09 ("mwifiex: update set_mac_address logic")
Signed-off-by: Brian Norris <briannorris@chromium.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>