Fix when reusing the same context for another operation.

Occurs in hmac, where multiple hashes are performed with the same context) and thus, it requires to reinitialize the internal states to 0.

Signed-off-by: Pol Henarejos <pol.henarejos@cttc.es>

library/sha3.c

@@ -212,6 +212,9 @@ int mbedtls_sha3_starts( mbedtls_sha3_context *ctx, mbedtls_sha3_id id )
     ctx->xor_byte = p->xor_byte;
     ctx->max_block_size = ctx->r / 8;
 
+    memset( ctx->state, 0, sizeof( ctx->state ) );
+    ctx->index = 0;
+
     return( 0 );
 }