ramips: fixup-mac-address: add missing include

Add missing include of ramips.sh in order to import the missing
ramips_board_name() procedure.

Fixes FS#774.

Signed-off-by: Jo-Philipp Wich <jo@mein.io>

target/linux/ramips/base-files/sbin/fixup-mac-address

@@ -1,6 +1,7 @@
 #!/bin/sh
 . /lib/functions.sh
 . /lib/functions/system.sh
+. /lib/ramips.sh
 
 partname=""
 offset=""