Crypto: Improve code quality

This patch fixes the following things:
* add const keyword when mutability is not required
* cast unused parameters/return values to void to be more explicit

Change-Id: I62471d95cc3249db2cf00fdd12c9634f12e99747
Signed-off-by: Hugues de Valon <hugues.devalon@arm.com>
diff --git a/secure_fw/services/crypto/crypto_key.c b/secure_fw/services/crypto/crypto_key.c
index 277ed10..499ffa7 100644
--- a/secure_fw/services/crypto/crypto_key.c
+++ b/secure_fw/services/crypto/crypto_key.c
@@ -10,9 +10,9 @@
 
 #include "tfm_crypto_api.h"
 #include "crypto_utils.h"
+#include "secure_fw/core/tfm_memory_utils.h"
 #include "psa_crypto.h"
 #include "tfm_crypto_defs.h"
-#include "secure_fw/core/tfm_memory_utils.h"
 
 /**
  * \brief This is the default value of maximum number of simultaneous
@@ -100,7 +100,7 @@
 enum tfm_crypto_err_t tfm_crypto_init_key(void)
 {
     /* Clear the contents of the local key_storage */
-    tfm_memset(key_storage, 0, sizeof(key_storage));
+    (void)tfm_memset(key_storage, 0, sizeof(key_storage));
     return TFM_CRYPTO_ERR_PSA_SUCCESS;
 }
 
@@ -275,6 +275,11 @@
                                                    size_t data_size,
                                                    size_t *data_length)
 {
+    (void)key;
+    (void)data;
+    (void)data_size;
+    (void)data_length;
+
     /* FIXME: This API is not supported yet */
     return TFM_CRYPTO_ERR_PSA_ERROR_NOT_SUPPORTED;
 }