ieee802154: make wpan-phy class registration to subsys_initcall

Move ieee802154 initialisation to subsys_initcall call, so that
wpan-phy class is initialised before all devices (thus saving us from
oops during bootup).

Signed-off-by: Dmitry Eremin-Solenikov <dbaryshkov@gmail.com>
diff --git a/net/ieee802154/wpan-class.c b/net/ieee802154/wpan-class.c
index 38bac70..2686912 100644
--- a/net/ieee802154/wpan-class.c
+++ b/net/ieee802154/wpan-class.c
@@ -205,7 +205,7 @@
 err:
 	return rc;
 }
-module_init(wpan_phy_class_init);
+subsys_initcall(wpan_phy_class_init);
 
 static void __exit wpan_phy_class_exit(void)
 {