mach-imx/mach-imx6ul.c: proper constness with __initconst

Both the pointer array and the pointed data have to be const when using
__initconst to be correct.  This also fixes LTO builds that otherwise
fail with section mismatch errors.
Signed-off-by: NNicolas Pitre <nico@linaro.org>
Signed-off-by: NShawn Guo <shawnguo@kernel.org>

arch/arm/mach-imx/mach-imx6ul.c

@@ -84,7 +84,7 @@ static void __init imx6ul_init_late(void)
 		platform_device_register_simple("imx6q-cpufreq", -1, NULL, 0);
 }
 
-static const char *imx6ul_dt_compat[] __initconst = {
+static const char * const imx6ul_dt_compat[] __initconst = {
 	"fsl,imx6ul",
 	NULL,
 };