usb: usbtmc: Add ioctl USBTMC_IOCTL_WRITE_RESULT

ioctl USBTMC_IOCTL_WRITE_RESULT copies current out_transfer_size
to given __u32 pointer and returns current out_status of the last
(asnynchronous) USBTMC_IOCTL_WRITE call.

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>