xo1-rfkill: only act when blocked state is changed

The XO-1 rfkill driver should only send EC commands when changing
between blocked/unblocked state.

The rfkill switch is asked to be unblocked on every resume (even when
the card was never blocked before) and sending a EC_WLAN_LEAVE_RESET
command here upsets the resume sequence of the libertas driver. Adding
the check to avoid the spurious EC_WLAN_LEAVE_RESET fixes the wifi resume
behaviour.

The rfkill state is maintained by the hardware over suspend/resume
so no extra consideration is needed here.

Signed-off-by: Daniel Drake <dsd@laptop.org>
Signed-off-by: Matthew Garrett <mjg@redhat.com>