device: Do not set regdom when device is not powered

device: Do not set regdom when device is not powered

Fixes crash bug:
connmand[6761]: plugins/ofono.c:get_properties_reply() /huawei_0 path /huawei_0 org.ofono.NetworkRegistration
connmand[6761]: plugins/ofono.c:netreg_properties_reply() /huawei_0
connmand[6761]: plugins/ofono.c:netreg_update_regdom() /huawei_0 MobileContryCode 460
connmand[6761]: src/device.c:connman_device_ref_debug() 0x8686ac0 ref 3 by plugins/wifi.c:991:wifi_set_regdom()
connmand[6761]: Aborting (signal 11) [src/connmand]
connmand[6761]: ++++++++ backtrace ++++++++
connmand[6761]: #0  0xb7749400 in
connmand[6761]: #1  0x806aa0b in g_supplicant_interface_set_country() at nat.c:0
connmand[6761]: #2  0x8062297 in wifi_set_regdom() at wifi.c:0
connmand[6761]: #3  0x80a607d in connman_technology_set_regdom() at ??:0
connmand[6761]: #4  0x806fefb in netreg_update_regdom() at ofono.c:0
connmand[6761]: #5  0x8071f3b in netreg_properties_reply() at ofono.c:0
connmand[6761]: #6  0x806f747 in get_properties_reply() at ofono.c:0
connmand[6761]: #7  0x4a374b62 in /usr/lib/libdbus-1.so.3
connmand[6761]: #8  0x4a3602b7 in /usr/lib/libdbus-1.so.3
connmand[6761]: #9  0x4a3639f5 in /usr/lib/libdbus-1.so.3
connmand[6761]: #10 0x8054250 in message_dispatch() at mainloop.c:0
connmand[6761]: #11 0x49f3e9d7 in /lib/libglib-2.0.so.0
connmand[6761]: #12 0x49f3de38 in /lib/libglib-2.0.so.0
connmand[6761]: #13 0x49f3e13e in /lib/libglib-2.0.so.0
connmand[6761]: #14 0x49f3e5a6 in /lib/libglib-2.0.so.0
connmand[6761]: #15 0x8053ab6 in main() at nat.c:0
connmand[6761]: #16 0x49cfc4c4 in /lib/libc.so.6
connmand[6761]: +++++++++++++++++++++++++++