fdformat prompts for user confirmation. it exits 0 if the user

doesn't confirm, which needlessly complicates scripts.

PR:		15339
Submitted by:	richard winkel rich@math.missouri.edu
MFC after:	1 week

usr.sbin/fdformat/fdformat.c

@@ -302,7 +302,7 @@ main(int argc, char **argv)
 			devname);
 		if(! yes ()) {
 			printf("Not confirmed.\n");
-			return 0;
+			return 3;
 		}
 	}