Fix dirty logging with 32-bit qemu & 64-bit guests

The kvm_get_dirty_pages_log_range() function uses two address
variables to step through the monitored memory region to update the
dirty log.  However, these variables have type unsigned long, which
can overflow if running a 64-bit guest with a 32-bit qemu binary.

This patch changes these to target_phys_addr_t which will have the
correct size.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Alexander Graf <agraf@suse.de>
