board: puma: use dtb given on the commandline instead of using u-boot.dtb

The make_fit_spl scripts get the dtb to use as commandline option,
so use it for puma as well.

Signed-off-by: Heiko Stuebner <heiko.stuebner@theobroma-systems.com>
diff --git a/board/theobroma-systems/puma_rk3399/fit_spl_atf.sh b/board/theobroma-systems/puma_rk3399/fit_spl_atf.sh
index 420e7da..c939657 100755
--- a/board/theobroma-systems/puma_rk3399/fit_spl_atf.sh
+++ b/board/theobroma-systems/puma_rk3399/fit_spl_atf.sh
@@ -69,7 +69,7 @@
                 };
 		fdt {
 			description = "RK3399-Q7 (Puma) flat device-tree";
-			data = /incbin/("u-boot.dtb");
+			data = /incbin/("$1");
 			type = "flat_dt";
 			compression = "none";
 		};