arm: mach-k3: am642_init: Add missing ddr guard

The `struct udevice *` reference is needed for either of the
K3_LOAD_SYSFW, K3_AM64_DDRSS config guards. Adding the missing
K3_AM64_DDRSS guard.
Signed-off-by: NGowtham Tammana <g-tammana@ti.com>
Signed-off-by: NLokesh Vutla <lokeshvutla@ti.com>
Link: https://lore.kernel.org/r/20210624171614.14244-1-g-tammana@ti.com

arch/arm/mach-k3/am642_init.c

@@ -141,7 +141,7 @@ int fdtdec_board_setup(const void *fdt_blob)
 
 void board_init_f(ulong dummy)
 {
-#if defined(CONFIG_K3_LOAD_SYSFW)
+#if defined(CONFIG_K3_LOAD_SYSFW) || defined(CONFIG_K3_AM64_DDRSS)
 	struct udevice *dev;
 	int ret;
 #endif