staging: comedi: addi_apci_3120: prevent deadlock in apci3120_ao_insn_write()

The DA_READY bit (0x0001) in the status register needs to be set before the
analog outputs can be updated.

Use comedi_timeout() to prevent a deadlock condition while waiting for the
DA_READY bit to get set.

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>