libata: cosmetic clean up in ata_eh_reset()

Local variable @action usage in ata_eh_reset() is a bit confusing.
It's used only to cache ehc->i.action to test reset masks after
clearing it; however, due to the generic name "action", it's easy to
misinterpret the local variable as containing the selected reset
method later.  Also, the reason for caching the original value is easy
to miss.

This patch renames @action to @tmp_action and make it buffer newly
selected value instead to improve readability.

Signed-off-by: Tejun Heo <htejun@gmail.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>