avm: fix sparse warning using integer as NULL pointer

drivers/isdn/hardware/avm/b1isa.c:206:37: warning: Using plain integer as NULL pointer
drivers/isdn/hardware/avm/b1isa.c:208:33: warning: Using plain integer as NULL pointer
drivers/isdn/hardware/avm/b1.c:664:42: warning: Using plain integer as NULL pointer
drivers/isdn/hardware/avm/b1.c:666:44: warning: Using plain integer as NULL pointer
drivers/isdn/hardware/avm/b1.c:668:42: warning: Using plain integer as NULL pointer
drivers/isdn/hardware/avm/b1.c:791:37: warning: Using plain integer as NULL pointer
drivers/isdn/hardware/avm/b1.c:793:33: warning: Using plain integer as NULL pointer
drivers/isdn/hardware/avm/b1pci.c:385:37: warning: Using plain integer as NULL pointer
drivers/isdn/hardware/avm/b1pci.c:387:33: warning: Using plain integer as NULL pointer
drivers/isdn/hardware/avm/b1dma.c:886:42: warning: Using plain integer as NULL pointer
drivers/isdn/hardware/avm/b1dma.c:888:44: warning: Using plain integer as NULL pointer
drivers/isdn/hardware/avm/b1dma.c:890:42: warning: Using plain integer as NULL pointer
drivers/isdn/hardware/avm/b1dma.c:973:37: warning: Using plain integer as NULL pointer
drivers/isdn/hardware/avm/b1dma.c:975:33: warning: Using plain integer as NULL pointer
drivers/isdn/hardware/avm/b1pcmcia.c:204:37: warning: Using plain integer as NULL pointer
drivers/isdn/hardware/avm/b1pcmcia.c:206:33: warning: Using plain integer as NULL pointer
drivers/isdn/hardware/avm/t1isa.c:554:37: warning: Using plain integer as NULL pointer
drivers/isdn/hardware/avm/t1isa.c:556:33: warning: Using plain integer as NULL pointer
drivers/isdn/hardware/avm/t1pci.c:236:37: warning: Using plain integer as NULL pointer
drivers/isdn/hardware/avm/t1pci.c:238:33: warning: Using plain integer as NULL pointer
drivers/isdn/hardware/avm/c4.c:1091:42: warning: Using plain integer as NULL pointer
drivers/isdn/hardware/avm/c4.c:1093:44: warning: Using plain integer as NULL pointer
drivers/isdn/hardware/avm/c4.c:1095:42: warning: Using plain integer as NULL pointer
drivers/isdn/hardware/avm/c4.c:1170:21: warning: Using plain integer as NULL pointer
drivers/isdn/hardware/avm/c4.c:1294:37: warning: Using plain integer as NULL pointer
drivers/isdn/hardware/avm/c4.c:1296:33: 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>