USB: xhci: properly set the "Mult" field of the endpoint context.

A SuperSpeed interrupt or isochronous endpoint can define the number of
"burst transactions" it can handle in a service interval.  This is
indicated by the "Mult" bits in the bmAttributes of the SuperSpeed
Endpoint Companion Descriptor.  For example, if it has a max packet size
of 1024, a max burst of 11, and a mult of 3, the host may send 33
1024-byte packets in one service interval.

We must tell the xHCI host controller the number of multiple service
opportunities (mults) the device can handle when the endpoint is
installed.  We do that by setting the Mult field of the Endpoint Context
before a configure endpoint command is sent down.  The Mult field is
invalid for control or bulk SuperSpeed endpoints.

Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>
Cc: stable <stable@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>