staging: comedi: s526: cleanup s526_gpct_winsn()

Use a local variable for the iobase of the channel being written.
This makes the outw() calls a bit cleaner.

Rearrange the switch () so that the actual write to the device
can be common regardless of the gpct configuration.

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>