Corrected the error introduced by commit afb400e of dropping
DATE/SRCDATE out of the vardepsexlude list of do_patch.
(From OE-Core rev: 6546096d068b51cc9cf4557cdb35aee6f62838d5)
Signed-off-by: Lianhao Lu <lianhao.lu@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>