usb: hcd: initialize hcd->flags to 0 when rm hcd

On some platforms(e.g. rk3399 board), we can call hcd_add/remove
consecutively without calling usb_put_hcd/usb_create_hcd in between,
so hcd->flags can be stale.

If the HC dies due to whatever reason then without this patch we get
the below error on next hcd_add.

[173.296154] xhci-hcd xhci-hcd.2.auto: HC died; cleaning up
[173.296209] xhci-hcd xhci-hcd.2.auto: xHCI Host Controller
[173.296762] xhci-hcd xhci-hcd.2.auto: new USB bus registered, assigned bus number 6
[173.296931] usb usb6: We don't know the algorithms for LPM for this host, disabling LPM.
[173.297179] usb usb6: New USB device found, idVendor=1d6b, idProduct=0003
[173.297203] usb usb6: New USB device strings: Mfr=3, Product=2, SerialNumber=1
[173.297222] usb usb6: Product: xHCI Host Controller
[173.297240] usb usb6: Manufacturer: Linux 4.4.21 xhci-hcd
[173.297257] usb usb6: SerialNumber: xhci-hcd.2.auto
[173.298680] hub 6-0:1.0: USB hub found
[173.298749] hub 6-0:1.0: 1 port detected
[173.299382] rockchip-dwc3 usb@fe800000: USB HOST connected
[173.395418] hub 5-0:1.0: activate --> -19
[173.603447] irq 228: nobody cared (try booting with the "irqpoll" option)
[173.603493] CPU: 0 PID: 0 Comm: swapper/0 Not tainted 4.4.21 #9
[173.603513] Hardware name: Google Kevin (DT)
[173.603531] Call trace:
[173.603568] [<ffffffc0002087dc>] dump_backtrace+0x0/0x160
[173.603596] [<ffffffc00020895c>] show_stack+0x20/0x28
[173.603623] [<ffffffc0004b28a8>] dump_stack+0x90/0xb0
[173.603650] [<ffffffc00027347c>] __report_bad_irq+0x48/0xe8
[173.603674] [<ffffffc0002737cc>] note_interrupt+0x1e8/0x28c
[173.603698] [<ffffffc000270a38>] handle_irq_event_percpu+0x1d4/0x25c
[173.603722] [<ffffffc000270b0c>] handle_irq_event+0x4c/0x7c
[173.603748] [<ffffffc00027456c>] handle_fasteoi_irq+0xb4/0x124
[173.603777] [<ffffffc00026fe3c>] generic_handle_irq+0x30/0x44
[173.603804] [<ffffffc0002701a8>] __handle_domain_irq+0x90/0xbc
[173.603827] [<ffffffc0002006f4>] gic_handle_irq+0xcc/0x188
...
[173.604500] [<ffffffc000203700>] el1_irq+0x80/0xf8
[173.604530] [<ffffffc000261388>] cpu_startup_entry+0x38/0x3cc
[173.604558] [<ffffffc00090f7d8>] rest_init+0x8c/0x94
[173.604585] [<ffffffc000e009ac>] start_kernel+0x3d0/0x3fc
[173.604607] [<0000000000b16000>] 0xb16000
[173.604622] handlers:
[173.604648] [<ffffffc000642084>] usb_hcd_irq
[173.604673] Disabling IRQ rockchip-linux#228

Signed-off-by: William wu <wulf@rock-chips.com>
Acked-by: Roger Quadros <rogerq@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/core/hcd.c

@@ -3017,6 +3017,7 @@ void usb_remove_hcd(struct usb_hcd *hcd)
 	}
 
 	usb_put_invalidate_rhdev(hcd);
+	hcd->flags = 0;
 }
 EXPORT_SYMBOL_GPL(usb_remove_hcd);