staging: comedi: ni_tio: tidy up struct ni_gpct_device (*{write, read}_register)

For aesthetics, rename these callbacks to simply read/write. Change the
'unsigned' parameters to 'unsigned int'.

This fixes a number of checkpatch.pl issues:
WARNING: Prefer 'unsigned int' to bare use of 'unsigned'

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