spl: fit: constify the output parameter of spl_fit_get_image_name()

There is no need for it to be non-constant. Making it constant, allows to
return constant string without warning.

Signed-off-by: Jean-Jacques Hiblot <jjhiblot@ti.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/common/spl/spl_fit.c b/common/spl/spl_fit.c
index 5aeb952..9001731 100644
--- a/common/spl/spl_fit.c
+++ b/common/spl/spl_fit.c
@@ -46,7 +46,7 @@
  */
 static int spl_fit_get_image_name(const void *fit, int images,
 				  const char *type, int index,
-				  char **outname)
+				  const char **outname)
 {
 	const char *name, *str;
 	__maybe_unused int node;
@@ -101,7 +101,7 @@
 static int spl_fit_get_image_node(const void *fit, int images,
 				  const char *type, int index)
 {
-	char *str;
+	const char *str;
 	int err;
 	int node;
 
@@ -387,7 +387,7 @@
 {
 	int ret = 0;
 #if !CONFIG_IS_ENABLED(FIT_IMAGE_TINY)
-	char *name;
+	const char *name;
 	int node;
 
 	ret = spl_fit_get_image_name(fit, images, "loadables",