scsi: ufs-mediatek: Fix imprecise waiting time for ref-clk control

Currently ref-clk control timeout is implemented by jiffies. However
jiffies is not accurate enough thus "false timeout" may happen.

Use more accurate delay mechanism instead, i.e. ktime.

Link: https://lore.kernel.org/r/20200601104646.15436-2-stanley.chu@mediatek.com


Reviewed-by: Andy Teng <andy.teng@mediatek.com>
Reviewed-by: Avri Altman <avri.altman@wdc.com>
Signed-off-by: Stanley Chu <stanley.chu@mediatek.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>