staging: comedi: addi_apci_1564: add addi_watchdog dependency

With commit aed3f9d4 ("staging: comedi: addi_apci_1564:
absorb apci1564_reset()"), the apci 1564 driver has gained
a dependency on the addi watchdog module, which is not reflected
correctly in Kconfig, and that can lead to link errors
when the watchdog is disabled.

This adds an explicit 'select', like it is done in the other
addi apci drivers that need it.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Cc: H Hartley Sweeten <hsweeten@visionengravers.com>
Acked-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>