staging: r8188eu: merge two probereq_p2p functions

_issue_probereq_p2p is called only by issue_probereq_p2p. Merge the two
functions and remove the unused return value.

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/20221202092525.403887-2-martin@kaiser.cx
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>