ar71xx/image: fix imagesize of template tplink-8mlzma

The new image size is verified by a running tplink device and checked
against mktplinkfw source code.

Signed-off-by: Alexander Couzens <lynxis@fe80.eu>

SVN-Revision: 45488

target/linux/ar71xx/image/Makefile

@@ -153,7 +153,7 @@ endef
 define Device/tplink-8mlzma
 $(Device/tplink)
   TPLINK_FLASHLAYOUT := 8Mlzma
-  IMAGE_SIZE := 8000k
+  IMAGE_SIZE := 7936k
 endef
 
 define Device/tl-wdr4300-v1