Building of FIT images does not work.

The type is not set for generation of the FIT images, resulting
in no images being created without printing or returning an error

Signed-off-by: Remy Bohmer <linux@bohmer.net>
diff --git a/tools/mkimage.c b/tools/mkimage.c
index ab6ea32..8a20594 100644
--- a/tools/mkimage.c
+++ b/tools/mkimage.c
@@ -229,6 +229,7 @@
 			case 'f':
 				if (--argc <= 0)
 					usage ();
+				params.type = IH_TYPE_FLATDT;
 				params.datafile = *++argv;
 				params.fflag = 1;
 				goto NXTARG;