staging: comedi: vmk80xx: factor out usb endpoint detection

Factor the code that detects the usb endpoints out of vmk80xx_usb_probe().

Cleanup the detection code in the new function,

Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Cc: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>