PCI: Check if entry->offset already exist for mem resource

LoongArch inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I6BWFP

--------------------------------

Fix patch "LoongArch: Add PCI controller support"
Signed-off-by: NTianli Xiong <xiongtianli@loongson.cn>
Change-Id: I796b1224d8990fed952643adac491228d6541696
(cherry picked from commit 4fcec201)

arch/loongarch/pci/acpi.c

@@ -210,9 +210,11 @@ static int acpi_prepare_root_resources(struct acpi_pci_root_info *ci)
 	if (status > 0) {
 		resource_list_for_each_entry_safe(entry, tmp, &ci->resources) {
 			if (entry->res->flags & IORESOURCE_MEM) {
-				entry->offset = ci->root->mcfg_addr & GENMASK_ULL(63, 40);
-				entry->res->start |= entry->offset;
-				entry->res->end   |= entry->offset;
+				if(!entry->offset) {
+					entry->offset = ci->root->mcfg_addr & GENMASK_ULL(63, 40);
+					entry->res->start |= entry->offset;
+					entry->res->end   |= entry->offset;
+				}
 			}
 		}
 		return status;