verilog: Fixing usage of cell reserved word.

`cell` is a Verilog reserved word.

Signed-off-by: Tim 'mithro' Ansell <tansell@google.com>
tree: b6ed921baa302e1a1fe0c08037475f2d69858775
  1. cells/
  2. models/
  3. tech/
  4. timing/
  5. .gitignore
  6. LICENSE
  7. README.rst