Use the Mult and bMaxBurst values from the endpoint companion
descriptor to calculate the max length of an isoc transfer.

Add USB_SS_MULT macro to access Mult field of bmAttributes, at
Sarah's suggestion.

This patch should be queued for the 2.6.36 and 2.6.37 stable trees, since
those were the first kernels to have isochronous support for SuperSpeed
devices.
Signed-off-by: NPaul Zimmerman <paulz@synopsys.com>
Signed-off-by: NSarah Sharp <sarah.a.sharp@linux.intel.com>
Cc: stable@kernel.org