kconfig: incorrect 'len' field initialisation ?

1) The field 'len' of the 'gstr' structure seems to track the size of the memory
already allocated for the "growable string". So the value of this field should be
the same as the 'malloc()' just above, shouldn't it ?

Signed-off-by: Christophe Jaillet <christophe.jaillet@wanadoo.fr>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>