USB: document the 'u' flag for usb-storage quirks parameter

Commit d24d481b7d36 (usb-storage: Modify and export adjust_quirks so
that it can be used by uas) added the 'u' flag to the quirks module
parameter for usb-storage, but neglected to update the
documentation.  This patch adds the documentation.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Cc: stable <stable@vger.kernel.org>  # 3.15+
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --cc Documentation/kernel-parameters.txt
Simple merge