platform/x86: dell-wmi: Adjust wifi catcher to emit KEY_WLAN

Wifi catcher is a slider switch, that when slid past the on position
will emit an event that is intended for launching a wifi application
or applet when the machine is turned on.

Signed-off-by: Mario Limonciello <mario_limonciello@dell.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>