ec/lenovo/h8: Clear EC output queue before enablement

Sometimes (observed on Thinkpad T400s during cold boot) a few (only one
observed) garbage bytes may detained in the output queue of EC after power
up, and they should be cleared otherwise later communications will be
disrupted.

Change-Id: Id1733f7350232d0b10ac0d1bc912b62e7fa4da75
Signed-off-by: Bill XIE <persmule@gmail.com>
Reviewed-on: https://review.coreboot.org/22181
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Maximilian Schander <coreboot@mimoja.de>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-by: Patrick Rudolph <siro@das-labor.org>

src/ec/lenovo/h8/h8.c

@@ -196,6 +196,7 @@ static void h8_enable(struct device *dev)
 
 	dev->ops = &h8_dev_ops;
 
+	ec_clear_out_queue();
 	h8_log_ec_version();
 
 	/* Always enable I/O range 0x1600-0x160f and thermal management */