staging: comedi: ni_pcidio: use comedi_load_firmware()

Use comedi_load_firmware() instead of duplicating the code in a
private function.

This driver loads multiple firmware images to the device. Modify
comedi_load_firmware() to take a 'context' that is passed to the
firmware upload callback 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>