ACPICA: Tables: Fix invalid pointer accesses in acpi_tb_parse_root_table().

Linux XSDT validation mechanism backport has introduced a regreession:
  Commit: 671cc68dc61f029d44b43a681356078e02d8dab8
  Subject: ACPICA: Back port and refine validation of the XSDT root table.
There is a pointer still accessed after unmapping.

This patch fixes this issue.  Lv Zheng.

Fixes: 671cc68dc61f (ACPICA: Back port and refine validation of the XSDT root table.)
References: https://bugzilla.kernel.org/show_bug.cgi?id=73911
References: https://bugs.archlinux.org/task/39811
Signed-off-by: Lv Zheng <lv.zheng@intel.com>
Reported-and-tested-by: Bruce Chiarelli <mano155@gmail.com>
Reported-and-tested-by: Spyros Stathopoulos <spystath@gmail.com>
Signed-off-by: Bob Moore <robert.moore@intel.com>
Cc: 3.14+ <stable@vger.kernel.org> # 3.14+
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/acpi/acpica/tbutils.c

@@ -461,6 +461,7 @@ acpi_status __init acpi_tb_parse_root_table(acpi_physical_address rsdp_address)
 	u32 table_count;
 	struct acpi_table_header *table;
 	acpi_physical_address address;
+	acpi_physical_address rsdt_address;
 	u32 length;
 	u8 *table_entry;
 	acpi_status status;
@@ -488,11 +489,14 @@ acpi_status __init acpi_tb_parse_root_table(acpi_physical_address rsdp_address)
 		 * as per the ACPI specification.
 		 */
 		address = (acpi_physical_address) rsdp->xsdt_physical_address;
+		rsdt_address =
+		    (acpi_physical_address) rsdp->rsdt_physical_address;
 		table_entry_size = ACPI_XSDT_ENTRY_SIZE;
 	} else {
 		/* Root table is an RSDT (32-bit physical addresses) */
 
 		address = (acpi_physical_address) rsdp->rsdt_physical_address;
+		rsdt_address = address;
 		table_entry_size = ACPI_RSDT_ENTRY_SIZE;
 	}
 
@@ -515,8 +519,7 @@ acpi_status __init acpi_tb_parse_root_table(acpi_physical_address rsdp_address)
 
 			/* Fall back to the RSDT */
 
-			address =
-			    (acpi_physical_address) rsdp->rsdt_physical_address;
+			address = rsdt_address;
 			table_entry_size = ACPI_RSDT_ENTRY_SIZE;
 		}
 	}