fdt_support: board_fdt_chosen_bootargs() should return const char*

It should be structured this way to demonstrate to the caller that
freeing the return value is unnecessary and that the caller cannot
modify it.
The function fdt_setprop() includes a parameter with a const char*
prototype, so it is better to use the const qualifier.

Signed-off-by: Dmitry Rokosov <ddrokosov@salutedevices.com>
Reviewed-by: Heinrich Schuchardt <xypron.glpk@gmx.de>

boot/fdt_support.c

@@ -321,7 +321,7 @@ int fdt_kaslrseed(void *fdt, bool overwrite)
  * board_fdt_chosen_bootargs - boards may override this function to use
  *                             alternative kernel command line arguments
  */
-__weak char *board_fdt_chosen_bootargs(void)
+__weak const char *board_fdt_chosen_bootargs(void)
 {
 	return env_get("bootargs");
 }
@@ -331,7 +331,7 @@ int fdt_chosen(void *fdt)
 	struct abuf buf = {};
 	int   nodeoffset;
 	int   err;
-	char  *str;		/* used to set string properties */
+	const char *str;		/* used to set string properties */
 
 	err = fdt_check_header(fdt);
 	if (err < 0) {

include/fdt_support.h

@@ -236,7 +236,7 @@ int board_rng_seed(struct abuf *buf);
  *
  * Return: pointer to kernel command line arguments in memory
  */
-char *board_fdt_chosen_bootargs(void);
+const char *board_fdt_chosen_bootargs(void);
 
 /*
  * The keystone2 SOC requires all 32 bit aliased addresses to be converted