libata: fix EH action overwriting in ata_eh_reset()

ehc->i.action got accidentally overwritten to ATA_EH_HARD/SOFTRESET in
ata_eh_reset().  The original intention was to clear reset action
which wasn't selected.  This can cause unexpected behavior when other
EH actions are scheduled together with reset.  Fix it.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>