scsi: ufs-mediatek: use common delay function

A common delay function is introduced in UFS core driver, thus ufs-mediatek
can use it instead of the private delay function.

Link: https://lore.kernel.org/r/20200318104016.28049-5-stanley.chu@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>