staging: comedi: hwdrv_apci1564: remove magic number in apci1564_timer_insn_read()

Use the bit define from addi_tcw.h to remove the magic number.

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>