tools/mkimage: Assume FDT image type for FIT images

When building a Flattened Image Tree (FIT) the image type needs to be
"flat_dt".  Commit 89a4d6b12f introduced a
regression which caused the user to need to specify the "-T flat_dt"
parameter on the command line when building a FIT image.  The "-T
flat_dt" parameter should not be needed and is at odds with the current
FIT image documentation.

Signed-off-by: Peter Tyser <ptyser@xes-inc.com>

tools/mkimage.c

@@ -232,6 +232,12 @@ main (int argc, char **argv)
 				params.type = IH_TYPE_FLATDT;
 				params.datafile = *++argv;
 				params.fflag = 1;
+
+				/*
+				 * The flattened image tree (FIT) format
+				 * requires a flattened device tree image type
+				 */
+				params.type = IH_TYPE_FLATDT;
 				goto NXTARG;
 			case 'n':
 				if (--argc <= 0)