kconfig: fix file name and line number of warn_ignored_character()

Currently, warn_ignore_character() displays invalid file name and
line number.

The lexer should use current_file->name and yylineno, while the parser
should use zconf_curname() and zconf_lineno().

This difference comes from that the lexer is always going ahead
of the parser. The parser needs to look ahead one token to make a
shift/reduce decision, so the lexer is requested to scan more text
from the input file.

This commit fixes the warning message from warn_ignored_character().

[Test Code]

  ----(Kconfig begin)----
  /
  -----(Kconfig end)-----

[Output]

  Before the fix:

  <none>:0:warning: ignoring unsupported character '/'

  After the fix:

  Kconfig:1:warning: ignoring unsupported character '/'

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>