Add explicit module search path to the verilator linter (#5000)

Adds the origin file directory as a module search path.
This is the default behaviour, this commit makes it explicit.

Note from the doc:

'-I' -> include search path
'-y' -> module search path

The space after '-y' seems mandatory, at least when I tested it with
vresion 5.032-46-g447ab12ce

ale_linters/verilog/verilator.vim

@@ -10,6 +10,7 @@ function! ale_linters#verilog#verilator#GetCommand(buffer) abort
     " the path to the current file is systematically added to the search path
     return 'verilator --lint-only -Wall -Wno-DECLFILENAME '
     \   . '-I%s:h '
+    \   . '-y %s:h '
     \   . ale#Var(a:buffer, 'verilog_verilator_options') .' '
     \   . '%t'
 endfunction