This patch fixes following sparse warnings:

include/linux/kfifo.h:127:25: warning: Using plain integer as NULL pointer
kernel/kfifo.c:83:21: warning: Using plain integer as NULL pointer
Signed-off-by: NAnton Vorontsov <avorontsov@ru.mvista.com>
Acked-by: NStefani Seibold <stefani@seibold.net>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>