scsi: ufs: ufs-mediatek: Prevent device regulators setting LPM incorrectly

Device regulatrs are allowed to enter low-power mode if neither device is
not in active mode, nor VCC does not keep on.

Fix this by adding conditions before LPM decision.

Link: https://lore.kernel.org/r/20220616053725.5681-6-stanley.chu@mediatek.com
Reviewed-by: Stanley Chu <stanley.chu@mediatek.com>
Signed-off-by: Po-Wen Kao <powen.kao@mediatek.com>
Signed-off-by: Stanley Chu <stanley.chu@mediatek.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>