mvebu: turris_omnia: use u-boot-spl-dtb.bin

u-boot-spl.bin and u-boot-spl-dtb.bin are identical when building the
turris_omnia_defconfig. This commit makes Turris Omnia consistent with
all other mvebu boards.

Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Stefan Roese <sr@denx.de>

board/CZ.NIC/turris_omnia/kwbimage.cfg

@@ -9,4 +9,4 @@ VERSION		1
 BOOT_FROM	spi
 
 # Binary Header (bin_hdr) with DDR3 training code
-BINARY spl/u-boot-spl.bin 0000005b 00000068
+BINARY spl/u-boot-spl-dtb.bin 0000005b 00000068