realtek: fix default image generation

realtek: fix default image generation

While cleaning up the makefiles for the realtek target, the order of the
default image generating commands was accidentally changed. This caused
the image signature to end up somewhere in the middle, misaligning the
rootfs. As a result, sysupgrade couldn't verify upgrade images anymore,
and devices end up in a boot loop due to the unaligned (and not found)
rootfs.

Fixes: 94d8b4852b9f ("realtek: Cleanup Makefiles")
Signed-off-by: Sander Vanheule <sander@svanheule.net>