ACPI: suppress uninitialized var warning

drivers/acpi/tables/tbutils.c: In function `acpi_tb_parse_root_table':
drivers/acpi/tables/tbutils.c:403: warning: `rsdt_address' may be used uninitialized in this function

Reported-by: Uwe Bugla <uwe.bugla@gmx.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Len Brown <len.brown@intel.com>