USB: dwc3: Fix issues in isochronous endpoint handling

If there are no requests queued by function driver when
XFRNRDY interrupt is recieved, pending flag will be set.
Then if function driver queues request, don't queue ENDTXFR
command and wait for XFRNRDY interrupt.

START TRANSFER command will fail if the interval for which
requests are being queued is already expired. Handle this
case by queueing ENDXFER command and waiting till recieves
XFRNRDY interrupt.

Change-Id: I9498be3967e0f80b05cf0830affe5463f07e2976
Signed-off-by: Vijayavardhan Vennapusa <vvreddy@codeaurora.org>