dell-laptop: Do not cache hwswitch state

The hwswitch state can be changed at runtime, so make sure dell-laptop
always knows the current state. It can be modified by the userspace
utility smbios-wireless-ctl.

Signed-off-by: Pali Rohár <pali.rohar@gmail.com>
Signed-off-by: Darren Hart <dvhart@linux.intel.com>