xen/unpopulated-alloc: fix error return code in fill_list()

Fix to return a negative error code from the error handling case instead
of 0, as done elsewhere in this function.

Fixes: a4574f6 ("mm/memremap_pages: convert to 'struct range'")
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
Reviewed-by: Juergen Gross <jgross@suse.com>
Link: https://lore.kernel.org/r/20210508021913.1727-1-thunder.leizhen@huawei.com
Signed-off-by: Juergen Gross <jgross@suse.com>

Author: Zhen Lei

drivers/xen/unpopulated-alloc.c

@@ -39,8 +39,10 @@ static int fill_list(unsigned int nr_pages)
 	}
 
 	pgmap = kzalloc(sizeof(*pgmap), GFP_KERNEL);
-	if (!pgmap)
+	if (!pgmap) {
+		ret = -ENOMEM;
 		goto err_pgmap;
+	}
 
 	pgmap->type = MEMORY_DEVICE_GENERIC;
 	pgmap->range = (struct range) {