ramips: use correct parameters in the Seama template

ramips: use correct parameters in the Seama template

Fixes DIR-645 image generation errors:

  bash: line 0: [: wrgn39_dlob.hans_dir645: integer expression expected
  ...
  bash: wrgn39_dlob.hans_dir645 - 64: syntax error: invalid arithmetic operator (error token is ".hans_dir645 - 64")  make[4]: *** [install] Error 1

Signed-off-by: Michael Lee <igvtee@gmail.com>
Signed-off-by: Gabor Juhos <juhosg@openwrt.org>
git-svn-id: svn://svn.openwrt.org/openwrt/trunk@37828 3c298f89-4303-0410-b956-a3cf2f4a3e73