kconfig: fix whitespace handling bug of savedefconfig

Commit 3ff291f3
(kconfig: convert Kconfig helper script into a shell script)
introduced another regression.

Shell usually handles whitespaces as separators,
so "make saveconfig" outputs

  # CONFIG_FOO is not set

into:

  #
  CONFIG_FOO
  is
  not
  set

Whitespaces should not be treated as separators here.

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
Acked-by: Simon Glass <sjg@chromium.org>