arm: mvebu: db-mv784mp-gp.h: Fix image creation - use correct offset

Signed-off-by: Stefan Roese <sr@denx.de>

include/configs/db-mv784mp-gp.h

@@ -136,6 +136,7 @@
 #define CONFIG_SPL_SPI_BUS		0
 #define CONFIG_SPL_SPI_CS		0
 #define CONFIG_SYS_SPI_U_BOOT_OFFS	0x20000
+#define CONFIG_SYS_U_BOOT_OFFS		CONFIG_SYS_SPI_U_BOOT_OFFS
 
 /* Enable DDR support in SPL (DDR3 training from Marvell bin_hdr) */
 #define CONFIG_SYS_MVEBU_DDR_AXP