usb: usbtmc: Optimize usbtmc_read

Use new usbtmc_generic_read function to maximize bandwidth
during long data transfer. Also fix reading of zero length
packet (ZLP) or trailing short packet.
The maximum input transfer size is limited to INT_MAX (=2GB).
Also remove redundant return in send_request_dev_dep_msg_in().

Signed-off-by: Guido Kiener <guido.kiener@rohde-schwarz.com>
Reviewed-by: Steve Bayless <steve_bayless@keysight.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>