staging: wfx: reduce hold duration of cfg80211_bss

Pointer to cfg80211_bss is held during all duration of wfx_do_join. But,
it is not necessary, We can release it far earlier.

Signed-off-by: Jérôme Pouiller <jerome.pouiller@silabs.com>
Link: https://lore.kernel.org/r/20200410133239.438347-3-Jerome.Pouiller@silabs.com


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