platform/x86: hp-wmi: Cleanup wireless get_(hw|sw)state functions

Use the new hp_wmi_read_int() function and add a WARN_ONCE() to the TBD
regarding passing the error through. These are used in a null return
function unfortunately.

Signed-off-by: Darren Hart (VMware) <dvhart@infradead.org>
Tested-by: Carlo Caione <carlo@endlessm.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>