scsi: ufs: fix default power mode to FAST/SLOW

We would by default like to run in FAST/SLOW mode instead
of FASTAUTO/SLOWAUTO mode for performance reasons. This
change sets the default speed mode to FAST/SLOW mode.

Reviewed-by: Venkat Gopalakrishnan <venkatg@codeaurora.org>
Signed-off-by: Subhash Jadavani <subhashj@codeaurora.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>