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/interface/src/tfm_crypto_api.c b/interface/src/tfm_crypto_api.c
index 9d28d5b..1ee71d8 100644
--- a/interface/src/tfm_crypto_api.c
+++ b/interface/src/tfm_crypto_api.c
@@ -83,6 +83,11 @@
                                    size_t data_size,
                                    size_t *data_length)
 {
+    (void)key;
+    (void)data;
+    (void)data_size;
+    (void)data_length;
+
     /* TODO: This API is not supported yet */
     return PSA_ERROR_NOT_SUPPORTED;
 }