staging: wfx: simplify handling of tx_lock in wfx_do_join()

In the old days, wfx_do_join() could be called from different contexts.
Now that wfx_do_join() is called only from one place, it is cleaner to
keep lock and unlock of data inside the function.

Signed-off-by: Jérôme Pouiller <jerome.pouiller@silabs.com>
Link: https://lore.kernel.org/r/20191217161318.31402-30-Jerome.Pouiller@silabs.com


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