ddconvnotrunc: Fix use of undefined IF_FILE variable

This is represented by ARG_IF if ARG_IF is not empty.

Signed-off-by: Andrew Jeffery <andrew@aj.id.au>
Change-Id: I05d68833f5a776f7f71f9e23f957d7fd0478afba
diff --git a/amboar/obmc-scripts/ddconvnotrunc/ddconvnotrunc b/amboar/obmc-scripts/ddconvnotrunc/ddconvnotrunc
index 12bc4cb..f2278bf 100755
--- a/amboar/obmc-scripts/ddconvnotrunc/ddconvnotrunc
+++ b/amboar/obmc-scripts/ddconvnotrunc/ddconvnotrunc
@@ -115,7 +115,7 @@
 then
 	cat >> "$OF_FILE"
 else
-	cat < "$IF_FILE" >> "$OF_FILE"
+	cat < "$ARG_IF" >> "$OF_FILE"
 fi
 OF_SUFFIX_OFF=$(filesize "$OF_FILE")