verilog-library-extensions

verilog-library-extensions is a variable defined in `verilog-mode.el'.
Its value is

(".v" ".sv")

• This variable is safe as a file local variable if its value
  satisfies the predicate `listp'.

Documentation:
List of extensions to use when looking for files for /*AUTOINST*/.
See also `verilog-library-flags', `verilog-library-directories'.

You can customize this variable.