[source] ramips: fix Airlink AR725W factory image build

[LEDE Commits]

mkresin pushed a commit to source.git, branch master:
https://git.lede-project.org/1ba7fa652cffffabb77f23a4d745633050c5c175

commit 1ba7fa652cffffabb77f23a4d745633050c5c175
Author: Mathias Kresin <dev at kresin.me>
AuthorDate: Sat Feb 4 11:02:36 2017 +0100

    ramips: fix Airlink AR725W factory image build
    
    The factory image can't be bigger than 3328 KByte. If the image is
    bigger than that, the gemtek-header tool throws an error and breaks
    the build.
    
    Make sure the output file to which the gemtek header should be added
    exists and wasn't removed during the check-size step because of it
    size. This will prevent hard errors in case the factory image is to big
    similar to what is done for sysupgrade images.
    
    Signed-off-by: Mathias Kresin <dev at kresin.me>
---
 target/linux/ramips/image/rt288x.mk | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/target/linux/ramips/image/rt288x.mk b/target/linux/ramips/image/rt288x.mk
index fbe50a2..33830a6 100644
--- a/target/linux/ramips/image/rt288x.mk
+++ b/target/linux/ramips/image/rt288x.mk
@@ -3,7 +3,10 @@
 #
 
 define Build/gemtek-header
-	mkheader_gemtek $@ $@.new $(1) && mv $@.new $@
+	if [ -f $@ ]; then \
+		mkheader_gemtek $@ $@.new $(1) && \
+		mv $@.new $@; \
+	fi
 endef
 
 define Device/ar670w
@@ -22,7 +25,7 @@ define Device/ar725w
   DTS := AR725W
   DEVICE_TITLE := Gemtek AR725W
   IMAGES += factory.bin
-  IMAGE/factory.bin := $$(sysupgrade_bin) | check-size $$$$(IMAGE_SIZE) | \
+  IMAGE/factory.bin := $$(sysupgrade_bin) | check-size 3328k | \
 	gemtek-header ar725w
 endef
 TARGET_DEVICES += ar725w