If request was already started, this means we had to
stop the transfer. With that we also need to ignore
all TRBs used by the request, however TRBs can only
be modified after completion of END_TRANSFER
command. So what we have to do here is wait for
END_TRANSFER completion and only after that jump
over TRBs by clearing HWO and incrementing dequeue
pointer.

Note that we have 2 possible types of transfers
here:

i) Linear buffer request
ii) SG-list based request

SG-list based requests will have r->num_pending_sgs
set to a valid number (> 0). Linear requests,
normally use a single TRB.

For each of these two cases, if r->unaligned flag is
set, one extra TRB has been used to align transfer
size to wMaxPacketSize.

All of these cases need to be taken into
consideration so we don't mess up our TRB ring
pointers.
Tested-by: Janusz Dziedzic <januszx.dziedzic@intel.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>