Return from bt_rfkill_poll() when hci_get_radio_state() fails.

value is invalid in that case and should not be assigned to the rfkill
state.

This also fixes a double unlock bug.
Signed-off-by: Jiri Slaby <jirislaby@gmail.com>
Cc: John W. Linville <linville@tuxdriver.com>
Cc: Johannes Berg <johannes@sipsolutions.net>
Cc: Henrique de Moraes Holschuh <hmh@hmh.eng.br>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Len Brown <len.brown@intel.com>