staging: r8188eu: remove DoReserved prototype

The DoReserved function was removed in commit 869ddbfc ("staging:
r8188eu: remove dummy entries from OnAction_tbl"). Remove the prototype
as well.

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/20220724153349.138741-3-martin@kaiser.cx


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