w1: omap-hdq: don't hardcode resource size

we have the helpful resource_size() macro to
calculate the size of the memory resource for
us, let's use it.

Signed-off-by: Felipe Balbi <balbi@ti.com>
Acked-by: Evgeniy Polyakov <zbr@ioremap.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>