Fix memory leak in hmp_info_vcpu_dirty_limit,use g_autoptr
to handle memory deallocation.

Signed-off-by: alloc.young <alloc.young@outlook.com>
Reviewed-by: Hyman Huang <yong.huang@smartx.com>
Message-Id: <SA1PR11MB6760B9AB7EAFBDAFB524ED06F5E3A@SA1PR11MB6760.namprd11.prod.outlook.com>
Signed-off-by: Hyman Huang <yong.huang@smartx.com>