Input: switch to using seq_list_xxx helpers

This is essentially just a renaming of the existing functions
as copies of seq_list_start() and seq_list_next() already existed
in the input.c.

Signed-off-by: Pavel Emelianov <xemul@openvz.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>