SMDK5250: Fix compiler warning for non-dt systems

Compiling for non-dt systems gives folowing warning:
smdk5250.c: In function 'board_eth_init':
smdk5250.c:152:6: warning: unused variable 'node' [-Wunused-variable]

Declare variable 'node' only for dt enabled systems to remove this
warning.

Signed-off-by: Vivek Gautam <gautam.vivek@samsung.com>
Acked-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Minkyu Kang <mk7.kang@samsung.com>

board/samsung/smdk5250/smdk5250.c

@@ -312,9 +312,10 @@ int board_eth_init(bd_t *bis)
 	u32 smc_bw_conf, smc_bc_conf;
 	struct fdt_sromc config;
 	fdt_addr_t base_addr;
-	int node;
 
 #ifdef CONFIG_OF_CONTROL
+	int node;
+
 	node = decode_sromc(gd->fdt_blob, &config);
 	if (node < 0) {
 		debug("%s: Could not find sromc configuration\n", __func__);