sata_dwc_460ex: re-use hsdev->dev instead of dwc_dev

This patch re-uses hsdev->dev which is allocated on heap. Therefore, the
private structure, which is global variable, is reduced by one field.

In one case ap->dev is used and there it seems to be right decision.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Tejun Heo <tj@kernel.org>