kconfig: made check-lxdialog more portable

OS-X shell did not like 'echo -e' so implement
suggestion from Al Viro to use a more portable construct.

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Cc: Al Viro <viro@ZenIV.linux.org.uk>
Acked-By: Timur Tabi <timur@freescale.com>