staging: comedi: pcmmio: introduce pcmmio_dio_write()

The paged registers in the asic need to be spinlock protected to
ensure that the page is not changed while writing to the registers.

Introduce a helper function to make sure the spinlock is used.

Use the new helper in pcmmio_reset(). This is one of the places where
the spinlock is not used.

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>