rfkill-gpio: Use gpio cansleep version

If gpio controller requires waiting for read and write
GPIO values, then we have to use the gpio cansleep api.
Fix the rfkill_gpio_set_power which calls only the
nonsleep version (causing kernel warning).
There is no problem to use the cansleep version here
because we are not in IRQ handler or similar context
(cf rfkill_set_block).

Signed-off-by: Loic Poulain <loic.poulain@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>