columbia: Update to the latest imx-mkimage tree

Change-Id: I778f6cbd520552d23cf0f7045df985e8a1488950
diff --git a/columbia.xml b/columbia.xml
index 21e9f53..d1a1584 100644
--- a/columbia.xml
+++ b/columbia.xml
@@ -8,7 +8,7 @@
     <!-- END prebuilts -->
 
     <!-- BEGIN imx specific build tools -->
-    <project path="tools/imx-mkimage" name="imx-mkimage" />
+    <project path="tools/imx-mkimage" name="imx-mkimage" branch="imx_4.9.123_imx8mm_ga" />
     <project path="packages/imx-mkimage" name="imx-mkimage-debian" />
     <!-- END imx specific build tools -->