toradex: common: Remove #ifdef usage for 2nd ethaddr

Fix checkpatch warn, use `IS_ENABLED(CONFIG_TDX_CFG_BLOCK_2ND_ETHADDR)`
instead of `#ifdef CONFIG_TDX_CFG_BLOCK_2ND_ETHADDR`.

Signed-off-by: Francesco Dolcini <francesco.dolcini@toradex.com>
diff --git a/board/toradex/common/tdx-common.c b/board/toradex/common/tdx-common.c
index 3643ebb..2284fcd 100644
--- a/board/toradex/common/tdx-common.c
+++ b/board/toradex/common/tdx-common.c
@@ -151,8 +151,8 @@
 	if (!eth_env_get_enetaddr("ethaddr", ethaddr))
 		eth_env_set_enetaddr("ethaddr", (u8 *)&tdx_eth_addr);
 
-#ifdef CONFIG_TDX_CFG_BLOCK_2ND_ETHADDR
-	if (!eth_env_get_enetaddr("eth1addr", ethaddr)) {
+	if (IS_ENABLED(CONFIG_TDX_CFG_BLOCK_2ND_ETHADDR) &&
+	    !eth_env_get_enetaddr("eth1addr", ethaddr)) {
 		/*
 		 * Secondary MAC address is allocated from block
 		 * 0x100000 higher then the first MAC address
@@ -161,7 +161,6 @@
 		ethaddr[3] += 0x10;
 		eth_env_set_enetaddr("eth1addr", ethaddr);
 	}
-#endif
 
 	return 0;
 }