xhci: fix placement of call to usb_disabled()

In the backport of 1eaf35e4dd592c59041bc1ed3248c46326da1f5f, the call to
usb_disabled() was too late, after we had already done some allocation.
Move that call to the top of the function instead, making the logic
match what is intended and is in the original patch.

Reported-by: Luis Henriques <luis.henriques@canonical.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>