rockchip: rk3588-coolpi: Fix .dtb-file entries in Makefile

Fix CoolPi 4 Model B and CoolPi CM5 EVB .dtb-file entries in Makefile.

Fixes: 3e15dee3 ("board: rockchip: Add support for rk3588 based Cool Pi CM5 EVB")
Signed-off-by: Jonas Karlman <jonas@kwiboo.se>
Reviewed-by: Dragan Simic <dsimic@manjaro.org>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>