board: stm32mp1: correct CONFIG_IS_ENABLED usage for LED

Use the correct macro to test presence CONFIG_LED:
replace CONFIG_IS_ENABLED(CONFIG_LED) by CONFIG_IS_ENABLED(LED)

Issue see during review unrelated patch
"board: stm32mp1: update management of boot-led"
http://patchwork.ozlabs.org/patch/1264823/

Cc: Marek Vasut <marex@denx.de>
Cc: Patrice Chotard <patrice.chotard@st.com>
Signed-off-by: NPatrick Delaunay <patrick.delaunay@st.com>
Reviewed-by: NMarek Vasut <marex@denx.de>
Reviewed-by: NPatrice Chotard <patrice.chotard@st.com>

board/dhelectronics/dh_stm32mp1/board.c

@@ -450,7 +450,7 @@ int board_init(void)
 
 	board_init_fmc2();
 
-	if (CONFIG_IS_ENABLED(CONFIG_LED))
+	if (CONFIG_IS_ENABLED(LED))
 		led_default_state();
 
 	return 0;

board/st/stm32mp1/stm32mp1.c

@@ -647,7 +647,7 @@ int board_init(void)
 
 	sysconf_init();
 
-	if (CONFIG_IS_ENABLED(CONFIG_LED))
+	if (CONFIG_IS_ENABLED(LED))
 		led_default_state();
 
 	return 0;