staging: wfx: drop useless checks in wfx_do_unjoin()

The callers of wfx_do_unjoin() already take care of vif state.
Therefore, it is not necessary to take care of the status of the
interface.

Signed-off-by: Jérôme Pouiller <jerome.pouiller@silabs.com>
Link: https://lore.kernel.org/r/20200420160311.57323-14-Jerome.Pouiller@silabs.com


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