rfkill: fix double-mutex-locking

rfkill_toggle_radio is called from functions where
rfkill->mutex is already aquired.

Remove the lock from rfkill_toggle_radio() and add it to
the only calling function that calls it without the lock held.

Signed-off-by: Michael Buesch <mb@bu3sch.de>
Acked-by: Ivo van Doorn <IvDoorn@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>