xen/privcmd: Fix a possible warning in privcmdioctlmmap_resource()
This is an automated ID intended to aid in discovery of potential security vulnerabilities. The actual impact and attack plausibility have not yet been proven. This ID is fixed in Linux Kernel version v5.15.86 by commit 0bf874183b32eae2cc20e3c5be38ec3d33e7e564, it was introduced in version v4.18 by commit 3ad0876554cafa368f574d4d408468510543e9ff. For more details please see the references link.