usb: xhci: Don't check for USB_STATE_NOTATTACHED in xhci_stop_endpoint

This API can be called by the QMI sound driver precisely when a
device is disconnected in order to issue a stop endpoint command
to properly halt the transfer ring. With this check the function
silently bails, so the XHCI controller hardware may continue to
be accessing the buffers on the transfer ring; meanwhile the
QMI sound driver proceeds to unmap the buffers from DMA
resulting in an SMMU fault. Remove the check to allow the
endpoint to be properly stopped.

Change-Id: I80315c31d9b1685ac4375c1da051a8e22cab07ca
Signed-off-by: Jack Pham <jackp@codeaurora.org>