Fix the build for example Hybrid City 10000

[jmackay2]

Issue:

When building, I get the following error:

gtsam/examples/Hybrid_City10000.cpp:113:35: error: cannot convert ‘size_t’ {aka ‘long unsigned int’} to ‘const gtsam::Values&’
  113 |     smoother_.update(*linearized, maxNrHypotheses);
      |                                   ^~~~~~~~~~~~~~~
      |                                   |
      |                                   size_t {aka long unsigned int}

Instead of using the size_t, this changes it to use the Values called initial_.

[varunagrawal]

This actually needs some more work but that should be my responsibility. Thanks!