rfkill: remove/inline __rfkill_set_hw_state

__rfkill_set_hw_state() is only one used in rfkill_set_hw_state(), and
none of them are long or complicated, so merging the two makes the code
easier to read.

Signed-off-by: João Paulo Rechi Vita <jprvita@endlessm.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>