staging: comedi: pcmmio: use pcmmio_dio_{read, write}() in interrupt_pcmmio()

Use the helper functions to read/write the PCMMIO_PAGE_INT_ID registers. This
allows removing the need to lock/unlock the spinlock 'pagelock' and removes the
need for the for () loop that did the read/write of the 3 paged registers.

Also, remove the need for the 'got1' local variable by just returning 'IRQ_NONE'
if there are not interrupts pending.

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>