media: serial_ir: use the right type for a dma address

As warned by smatch:
	drivers/media/rc/serial_ir.c:550 serial_ir_probe() warn: should '8 << ioshift' be a 64 bit type?

the "8" constant should be unsigned long.

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