scsi: ufs: ufs-mediatek: Fix invalid access to vccqx

NULL pointer access issue was found for the regulator released
by ufs_mtk_vreg_fix_vccq(). Simply fix this issue by clearing
the released vreg pointer in ufs_hba struct.

Link: https://lore.kernel.org/r/20220623035052.18802-9-stanley.chu@mediatek.com
Reviewed-by: Stanley Chu <stanley.chu@mediatek.com>
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Alice Chao <alice.chao@mediatek.com>
Signed-off-by: Stanley Chu <stanley.chu@mediatek.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/ufs/host/ufs-mediatek.c

@@ -758,6 +758,7 @@ static void ufs_mtk_vreg_fix_vccqx(struct ufs_hba *hba)
 		regulator_disable((*vreg_off)->reg);
 		devm_kfree(hba->dev, (*vreg_off)->name);
 		devm_kfree(hba->dev, *vreg_off);
+		*vreg_off = NULL;
 	}
 }