whisper : reset ctx->t_start_us when calling whisper_reset_timings() (#1434)

Co-authored-by: Ben Nortier <ben@bjnortier.com>

whisper.cpp

@@ -3688,6 +3688,7 @@ void whisper_print_timings(struct whisper_context * ctx) {
 }
 
 void whisper_reset_timings(struct whisper_context * ctx) {
+    ctx->t_start_us = ggml_time_us();
     if (ctx->state != nullptr) {
         ctx->state->t_sample_us = 0;
         ctx->state->t_encode_us = 0;