eicon: fix sparse integer as NULL pointer warnings

drivers/isdn/hardware/eicon/message.c:745:47: warning: Using plain integer as NULL pointer
drivers/isdn/hardware/eicon/message.c:761:45: warning: Using plain integer as NULL pointer
drivers/isdn/hardware/eicon/message.c:9122:16: warning: Using plain integer as NULL pointer
drivers/isdn/hardware/eicon/message.c:9147:16: warning: Using plain integer as NULL pointer
drivers/isdn/hardware/eicon/message.c:9173:14: warning: Using plain integer as NULL pointer
drivers/isdn/hardware/eicon/divasmain.c:396:23: warning: Using plain integer as NULL pointer

Signed-off-by: Harvey Harrison <harvey.harrison@gmail.com>
Cc: Karsten Keil <kkeil@suse.de>
Cc: Jeff Garzik <jeff@garzik.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>