Fix kernel dimensions for LeNet model code example (#2192)

* Change kernel to 5x5 in  1st Conv2d layer in model init

Signed-off-by: Kiersten Stokes <kierstenstokes@gmail.com>

* Change kernel to 5x5 in 2nd Conv2d layer in model init

* Fix dimensions of 1st Linear layer to match new expected size

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Signed-off-by: Kiersten Stokes <kierstenstokes@gmail.com>
Co-authored-by: Suraj Subramanian <5676233+suraj813@users.noreply.github.com>
Co-authored-by: Svetlana Karslioglu <svekars@fb.com>

Author: 3 people