scsi: ufs-mediatek: Prevent LPM operation on undeclared VCC

In some platforms, VCC regulator may not be declared in device tree to keep
itself "always-on". In this case, hba->vreg_info.vcc is NULL and shall not
be operated during any flow.

Prevent possible NULL hba->vreg_info.vcc access in LPM mode by checking
if it is valid first.

Link: https://lore.kernel.org/r/20200724141627.20094-1-stanley.chu@mediatek.comReviewed-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>

drivers/scsi/ufs/ufs-mediatek.c

@@ -574,7 +574,7 @@ static int ufs_mtk_link_set_lpm(struct ufs_hba *hba)
 
 static void ufs_mtk_vreg_set_lpm(struct ufs_hba *hba, bool lpm)
 {
-	if (!hba->vreg_info.vccq2)
+	if (!hba->vreg_info.vccq2 || !hba->vreg_info.vcc)
 		return;
 
 	if (lpm & !hba->vreg_info.vcc->enabled)