[PATCH] ahci: do not fail softreset if PHY reports no device

All softreset methods are responsible for detecting device presence
and succeed softreset in such cases.  AHCI didn't use to check for
device presence before proceeding with softreset and this caused
unnecessary reset retrials during probing.  This patch adds presence
detection to AHCI softreset.

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