sony-laptop: Make sony_pic_set_wwanpower not take mutexes

For consistency with __sony_pic_set_bluetoothpower, this is also needed
later to allow setting the wwanpower attribute from the resume path and
only lock the mutex once.

Signed-off-by: Mattia Dongili <malattia@linux.it>
Signed-off-by: Len Brown <len.brown@intel.com>