staging: wfx: simplify wfx_tx_queue_mask_get()

It is far simpler to return a pointer instead of an error. Thus, it is
no more necessary to pass a pointer reference as argument.

Reviewed-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Jérôme Pouiller <jerome.pouiller@silabs.com>
Link: https://lore.kernel.org/r/20200401110405.80282-12-Jerome.Pouiller@silabs.com


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