Call mbedtls_platform_zeroize via mbedtls_sha3_free

Signed-off-by: Dave Rodgman <dave.rodgman@arm.com>
diff --git a/library/sha3.c b/library/sha3.c
index 9825504..dca5790 100644
--- a/library/sha3.c
+++ b/library/sha3.c
@@ -286,7 +286,7 @@
     ret = 0;
 
 exit:
-    mbedtls_platform_zeroize(ctx, sizeof(mbedtls_sha3_context));
+    mbedtls_sha3_free(ctx);
     return ret;
 }