ramips: fix Netgear EX2700 images

The previous image creation code would have failed if the
unpadded kernel uImage size was less than 64 bytes from the
next erase block boundary. Fix that.

Signed-off-by: Joseph C. Lehner <joseph.c.lehner@gmail.com>

target/linux/ramips/image/mt7620.mk

@@ -8,8 +8,9 @@ define Build/tplink-header
 endef
 
 define Build/pad-kernel-ex2700
-	dd if=$@ of=$@.new bs=64k conv=sync && truncate -s -64 $@.new \
-		&& cat ex2700-fakeroot.uImage >> $@.new && mv $@.new $@
+	dd if=/dev/zero of=$@.pad bs=64 count=1 && cat $@ $@.pad \
+		| dd of=$@.new bs=64k conv=sync && truncate -s -64 $@.new \
+		&& cat ex2700-fakeroot.uImage >> $@.new && rm $@.pad && mv $@.new $@
 endef
 
 define Build/netgear-header