xhci: Fix memory leak bug when dropping endpoints

When the USB core wants to change to an alternate interface setting that
doesn't include an active endpoint, or de-configuring the device, the xHCI
driver needs to issue a Configure Endpoint command to tell the host to
drop some endpoints from the schedule.  After the command completes, the
xHCI driver needs to free rings for any endpoints that were dropped.

Unfortunately, the xHCI driver wasn't actually freeing the endpoint rings
for dropped endpoints.  The rings would be freed if the endpoint's
information was simply changed (and a new ring was installed), but dropped
endpoints never had their rings freed.  This caused errors when the ring
segment DMA pool was freed when the xHCI driver was unloaded:

[ 5582.883995] xhci_hcd 0000:06:00.0: dma_pool_destroy xHCI ring segments, ffff88003371d000 busy
[ 5582.884002] xhci_hcd 0000:06:00.0: dma_pool_destroy xHCI ring segments, ffff880033716000 busy
[ 5582.884011] xhci_hcd 0000:06:00.0: dma_pool_destroy xHCI ring segments, ffff880033455000 busy
[ 5582.884018] xhci_hcd 0000:06:00.0: Freed segment pool
[ 5582.884026] xhci_hcd 0000:06:00.0: Freed device context pool
[ 5582.884033] xhci_hcd 0000:06:00.0: Freed small stream array pool
[ 5582.884038] xhci_hcd 0000:06:00.0: Freed medium stream array pool
[ 5582.884048] xhci_hcd 0000:06:00.0: xhci_stop completed - status = 1
[ 5582.884061] xhci_hcd 0000:06:00.0: USB bus 3 deregistered
[ 5582.884193] xhci_hcd 0000:06:00.0: PCI INT A disabled

Fix this issue and free endpoint rings when their endpoints are
successfully dropped.

This patch should be backported to kernels as old as 2.6.31.

Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>
Cc: stable@kernel.org