USB: usbtmc: Use usb_clear_halt() instead of custom code.

Make the USB Test & Measurement driver use usb_clear_halt() instead of
usb_control_msg() to clear a stalled endpoint.  This will allow devices to
be tested under an xHCI host controller.  The endpoint stall will not be
cleared in the internal xHCI hardware state unless usb_clear_halt() is
used.

Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>
Cc: Steve Holland <sdh4@iastate.edu>
Cc: Oliver Neukum <oliver@neukum.org>
Cc: Jouni Ryno <Jouni.Ryno@fmi.fi>
Cc: Gergely Imreh <imrehg@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>