[PATCH] ahci: cosmetic changes to ahci_start/stop_engine()

* fascist-format comments according to comment style used in libata
  core layer.

* if() -> if ()

Signed-off-by: Tejun Heo <htejun@gmail.com>
Signed-off-by: Zhao, Forrest <forrest.zhao@intel.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>