scsi: ufs: kick start clock scaling only after device detection

UFS clock scaling might start kicking in even before the device
is running at the fastest interface speed which is undesirable.
This change moves the clock scaling kick start only after the
device is detected and running at the fastest interface speed.

Change-Id: Id9af7b31eab5b67f4cf2eb38c4e90a568e7968c5
Signed-off-by: Subhash Jadavani <subhashj@codeaurora.org>
[cang@codeaurora.org: resolved trivial merge conflicts]
Signed-off-by: Can Guo <cang@codeaurora.org>