xen: use correct type for HYPERVISOR_memory_op()

xen: use correct type for HYPERVISOR_memory_op()

HYPERVISOR_memory_op() is defined to return an "int" value. This is
wrong, as the Xen hypervisor will return "long".

The sub-function XENMEM_maximum_reservation returns the maximum
number of pages for the current domain. An int will overflow for a
domain configured with 8TB of memory or more.

Correct this by using the correct type.

Signed-off-by: Juergen Gross <jgross@suse.com>
Signed-off-by: David Vrabel <david.vrabel@citrix.com>
(cherry picked from commit 24f775a6605a8ffc697c0767fc7ea85656ddb958)
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>