media: cx88-alsa: number of pages should be unsigned long

As reported by smatch:

	drivers/media/pci/cx88/cx88-alsa.c:286 cx88_alsa_dma_init() warn: should 'nr_pages << 12' be a 64 bit type?

the number of patches should be unsigned long.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>