hp-wmi: fix rfkill bug

Fix the third (I think) polarity error I accidentally
introduced in the rfkill rewrite to make wireless work
again on (certain?) HP laptops.

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Tested-by: Maciej Rutecki <maciej.rutecki@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>