CHROMIUM: usb: dwc3: rockchip: fix NULL pointer dereference when resume

CHROMIUM: usb: dwc3: rockchip: fix NULL pointer dereference when resume

During system PM resume process, if remove XHCI hcd prior to
XHCI controller PM resume, it will result in a crash with
the following backtrace.

[   80.730581] Unable to handle kernel NULL pointer dereference at virtual address 00000138
...
[   80.731780] Call trace:
[   80.731784] [<ffffffc0005e43cc>] dev_driver_string+0x18/0x4c
[   80.731787] [<ffffffc0005e4918>] __dev_printk+0x34/0x88
[   80.731791] [<ffffffc0005e4da0>] dev_warn+0x7c/0xa0
[   80.731796] [<ffffffc000651ef8>] usb_root_hub_lost_power+0x28/0x40
[   80.731801] [<ffffffc0006866e8>] xhci_resume+0x250/0x444
[   80.731805] [<ffffffc00069612c>] xhci_plat_resume+0x44/0x64
[   80.731811] [<ffffffc0005ea878>] platform_pm_resume+0x50/0x64
[   80.731816] [<ffffffc0005f6354>] dpm_run_callback+0xb0/0x198
[   80.731819] [<ffffffc0005f68f4>] device_resume+0x160/0x19c
[   80.731822] [<ffffffc0005f6960>] async_resume+0x30/0x60
[   80.731827] [<ffffffc000242b88>] async_run_entry_fn+0x50/0xfc
[   80.731832] [<ffffffc000238e38>] process_one_work+0x230/0x3dc
[   80.731837] [<ffffffc000239db8>] worker_thread+0x248/0x370
[   80.731840] [<ffffffc00023f23c>] kthread+0x10c/0x114
[   80.731845] [<ffffffc000203d90>] ret_from_fork+0x10/0x40

It's because that when do PM resume, dwc3_rockchip_resume() will
be called before XHCI resume, and it will remove XHCI hcd and set
rhdev->dev to NULL, this cause rhdev->dev NULL pointer dereference
in XHCI resume.

So we need to check the flag dwc->xhci->dev.power.is_suspended to
ensure that XHCI has been resumed completely from pm suspended state
before remove XHCI hcd.

BUG=chrome-os-partner:58705
TEST=Plug in Type-C USB device, then set system to enter S3.
After system suspend, plug out the Type-C USB device first,
and then press keyboard or power key to check if system can
wakeup successfully.

Change-Id: I90fc48f5d3af8d08a290861ad7fcdaa5e4352320
Signed-off-by: William wu <wulf@rock-chips.com>
Reviewed-on: https://chromium-review.googlesource.com/408498
Commit-Ready: Guenter Roeck <groeck@chromium.org>
Tested-by: Guenter Roeck <groeck@chromium.org>
Reviewed-by: Guenter Roeck <groeck@chromium.org>
Reviewed-by: Matthias Kaehlcke <mka@chromium.org>
Signed-off-by: William Wu <wulf@rock-chips.com>