staging: vt6655: update out-of-date function declaration

The function iwctl_siwscan() is defined in iwctl.c as:
int iwctl_siwscan(struct net_device *dev,
		  struct iw_request_info *info,
		  struct iw_point *wrq,
		  char *extra)
{
  ...

This patch updates iwctl.h so that the type of the 3rd parameter (*wqr) in the
function declaration matches the definition.

Signed-off-by: James A Shackleford <shack@linux.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>