Tsizer returns an error with -g2012

[dmitrystu]

Tsizer returns an error with the -g2012 option (as well as with -g2009 and -g2005-sv), showing the message:

SIZER: The root scope $unit must be a module.
error: Code generation had 1 error(s).

However, the output statistic was generated as well.
The code contains only modules and works without issues when using the default -g2005 option.

[caryr]

We likely just need to modify the code to skip the SystemVerilog $unit scope.