ARM: imx: mark .dt_compat as const

Otherwise GCC will mark the .init.rodata section R/W, which causes
a compile error once we add other real R/O data.

Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
Signed-off-by: Shawn Guo <shawn.guo@freescale.com>

arch/arm/mach-imx/mach-imx6sx.c

@@ -44,7 +44,7 @@ static void __init imx6sx_init_late(void)
 	imx6q_cpuidle_init();
 }
 
-static const char *imx6sx_dt_compat[] __initconst = {
+static const char * const imx6sx_dt_compat[] __initconst = {
 	"fsl,imx6sx",
 	NULL,
 };