staging: r8188eu: drop return value from issue_probereq_ex

The only caller of issue_probereq_ex does not check the return value. We
can remove it and make issue_probereq_ex a void function.

Tested-by: Philipp Hortmann <philipp.g.hortmann@gmail.com> # Edimax N150
Signed-off-by: Martin Kaiser <martin@kaiser.cx>
Link: https://lore.kernel.org/r/20221126154253.178275-2-martin@kaiser.cx


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