pciehp: Add missing memory barrier

Fix the possible race condition between pcie_isr() and pciehp_write_cmd()
because of the lack of memory barrier.

Signed-off-by: Kenji Kaneshige <[e-mail]>
Signed-off-by: Kristen Carlson Accardi <[e-mail]>
Signed-off-by: Jesse Barnes <[e-mail]>

drivers/pci/hotplug/pciehp_hpc.c

···
 	slot_ctrl |= ((cmd & mask) | CMD_CMPL_INTR_ENABLE);
 
 	ctrl->cmd_busy = 1;
+	smp_mb();
 	retval = pciehp_writew(ctrl, SLOTCTRL, slot_ctrl);
 	if (retval)
 		err("%s: Cannot write to SLOTCTRL register\n", __func__);
···
 	/* Check Command Complete Interrupt Pending */
 	if (intr_loc & CMD_COMPLETED) {
 		ctrl->cmd_busy = 0;
+		smp_mb();
 		wake_up_interruptible(&ctrl->queue);
 	}