scripts/Makefile.lib: Re-add -Wno-simple_bus_reg to DTC_FLAGS

This exists in Linux Kernel with commit 70523a3ce5ff so put it in the
list of DTC_FLAGS that mirror Linux as we will catch up there.

Signed-off-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Masahiro Yamada <masahiroy@kernel.org>
diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
index a819667..63d790e 100644
--- a/scripts/Makefile.lib
+++ b/scripts/Makefile.lib
@@ -280,6 +280,7 @@
 	-Wno-unit_address_format \
 	-Wno-avoid_unnecessary_addr_size \
 	-Wno-alias_paths \
+	-Wno-simple_bus_reg \
 	-Wno-pci_device_reg
 
 # U-Boot specific disables