libata: clear eh_info on reset completion

Resets are done with port frozen but some controllers still issue
interrupts during reset and they may end up recording error conditions
in ehi leading to unnecessary EH retrials.

This patch makes ata_eh_reset() clear ehi on reset completion.  As
reset is the most severe recovery action, there's nothing to lose by
clearing ehi on its completion.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-by: Zdenek Kaspar <zkaspar82@gmail.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>