staging: comedi: usbduxfast: move usbduxfast_upload_firmware()

For aesthetic reasons, move usbduxfast_upload_firmware() near its
only caller, usbduxfast_request_firmware().

Also, move the #define for the maximum firmware size so it's with
the other firmware defines.

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>