V4L/DVB (12993a): saa7164: Fix compilation warning on i386

drivers/media/video/saa7164/saa7164-buffer.c: In function ‘saa7164_buffer_alloc’:
drivers/media/video/saa7164/saa7164-buffer.c:110: warning: cast to pointer from integer of different size
drivers/media/video/saa7164/saa7164-buffer.c:112: warning: cast to pointer from integer of different size

Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>