lib: rsa: Fix const-correctness of rsassa_pss functions

Prior to introduction of modifications in rsassa_pss functions
related to padding verification, doing a pass to update
const-correctness in targeted functions to comply with
coding-rules and avoid const-cast

Signed-off-by: SESA644425 <gioja.hermann@non.se.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/include/u-boot/rsa.h b/include/u-boot/rsa.h
index b9634e3..085363e 100644
--- a/include/u-boot/rsa.h
+++ b/include/u-boot/rsa.h
@@ -101,11 +101,11 @@
 			 const void *hash, uint8_t *sig, uint sig_len);
 
 int padding_pkcs_15_verify(struct image_sign_info *info,
-			   uint8_t *msg, int msg_len,
+			   const uint8_t *msg, int msg_len,
 			   const uint8_t *hash, int hash_len);
 
 int padding_pss_verify(struct image_sign_info *info,
-		       uint8_t *msg, int msg_len,
+		       const uint8_t *msg, int msg_len,
 		       const uint8_t *hash, int hash_len);
 
 #define RSA_DEFAULT_PADDING_NAME		"pkcs-1.5"