xHCI host controllers can have both USB 3.1 and 3.0 extended speed
protocol lists. If the USB3.1 speed is parsed first and 3.0 second then
the minor revision supported will be overwritten by the 3.0 speeds and
the USB3 roothub will only show support for USB 3.0 speeds.

This was the case with a xhci controller with the supported protocol
capability listed below.
In xhci-mem.c, the USB 3.1 speed is parsed first, the min_rev of usb3_rhub
is set as 0x10.  And then USB 3.0 is parsed.  However, the min_rev of
usb3_rhub will be changed to 0x00. If USB 3.1 device is connected behind
this host controller, the speed of USB 3.1 device just reports 5G speed
using lsusb.

     00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F
  00 01 08 00 00 00 00 00 40 00 00 00 00 00 00 00 00
  10 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  20 02 08 10 03 55 53 42 20 01 02 00 00 00 00 00 00     //USB 3.1
  30 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  40 02 08 00 03 55 53 42 20 03 06 00 00 00 00 00 00     //USB 3.0
  50 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  60 02 08 00 02 55 53 42 20 09 0E 19 00 00 00 00 00     //USB 2.0
  70 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

This patch fixes the issue by only owerwriting the minor revision if
it is higher than the existing one.

[reword commit message -Mathias]
Cc: <stable@vger.kernel.org>
Signed-off-by: YD Tseng <yd_tseng@asmedia.com.tw>
Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>