USB: FHCI: upgrade the isochronous API

This patch attempts to fix the isochronous API in the fhci-hcd
driver.  There are two problems with the current code:

	ed->last_iso is used but not set anywhere.  The patch changes
	its name to ed->next_iso and uses it to store the frame number
	of the next available slot in the isochronous stream.

	urb->start_frame isn't set when the URB_ISO_ASAP flag is off.
	The patch sets it to the next available slot if the stream is
	in use, or the current frame otherwise.

This won't give the right behavior when an underrun occurs, but I
don't know enough about the driver to handle that case.

Unfortunately, I don't have any way to test these changes.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
CC: Anton Vorontsov <avorontsov@ru.mvista.com>
CC: Li Yang <leoli@freescale.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>