image-fit: Make string of algo parameter constant

Modifications would be invalid.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/boot/image-fit.c b/boot/image-fit.c
index f6594e0..85a6f22 100644
--- a/boot/image-fit.c
+++ b/boot/image-fit.c
@@ -191,7 +191,7 @@
 	const char *keyname;
 	uint8_t *value;
 	int value_len;
-	char *algo;
+	const char *algo;
 	const char *padding;
 	bool required;
 	int ret, i;
@@ -1063,11 +1063,11 @@
  *     0, on success
  *     -1, on failure
  */
-int fit_image_hash_get_algo(const void *fit, int noffset, char **algo)
+int fit_image_hash_get_algo(const void *fit, int noffset, const char **algo)
 {
 	int len;
 
-	*algo = (char *)fdt_getprop(fit, noffset, FIT_ALGO_PROP, &len);
+	*algo = (const char *)fdt_getprop(fit, noffset, FIT_ALGO_PROP, &len);
 	if (*algo == NULL) {
 		fit_get_debug(fit, noffset, FIT_ALGO_PROP, len);
 		return -1;
@@ -1265,7 +1265,7 @@
 {
 	uint8_t value[FIT_MAX_HASH_LEN];
 	int value_len;
-	char *algo;
+	const char *algo;
 	uint8_t *fit_value;
 	int fit_value_len;
 	int ignore;