scsi: ufs: Stop hardcoding the scale down gear

Instead of hardcoding the scale down gear, make it a member of
the ufs_clk_scaling struct.

Link: https://lore.kernel.org/r/1606442334-22641-1-git-send-email-cang@codeaurora.org


Reviewed-by: Stanley Chu <stanley.chu@mediatek.com>
Reviewed-by: Bean Huo <beanhuo@micron.com>
Reviewed-by: Asutosh Das <asutoshd@codeaurora.org>
Signed-off-by: Can Guo <cang@codeaurora.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>