usb: host: xhci: remove bogus __releases()/__acquires() annotation

handle_tx_event() is not releasing xhci->lock nor reacquiring it, remove
the bogus annotation.

Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>
Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>