kconfig: update current_pos in the second lexer

To simplify the generated lexer, let the hand-made lexer update the
file name and line number for the parser.

I tested this with DEBUG_PARSE, and confirmed the same file names
and line numbers were dumped.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Christian Lamparter <chunkeey@gmail.com>