ARM: stm32: Use __section(".data") with dot in the section name on DHSOM

The correct specifier of the section is ".data" and not "data",
use the former to place the variables in ".data" section.

Fixes: 731fd50e27f ("ARM: stm32: Implement board coding on AV96")
Fixes: 92ca0f7446c ("ARM: dts: stm32: Synchronize DDR setttings on DH SoMs")
Signed-off-by: Marek Vasut <marex@denx.de>
Reviewed-by: Patrice Chotard <patrice.chotard@foss.st.com>
Reviewed-by: Patrick Delaunay <patrick.delaunay@foss.st.com>
diff --git a/board/dhelectronics/dh_stm32mp1/board.c b/board/dhelectronics/dh_stm32mp1/board.c
index 8d8104a..f9cfabe 100644
--- a/board/dhelectronics/dh_stm32mp1/board.c
+++ b/board/dhelectronics/dh_stm32mp1/board.c
@@ -184,9 +184,9 @@
 }
 
 #ifdef CONFIG_BOARD_EARLY_INIT_F
-static u8 brdcode __section("data");
-static u8 ddr3code __section("data");
-static u8 somcode __section("data");
+static u8 brdcode __section(".data");
+static u8 ddr3code __section(".data");
+static u8 somcode __section(".data");
 static u32 opp_voltage_mv __section(".data");
 
 static void board_get_coding_straps(void)