staging: comedi: addi_eeprom: use AMCC_OP_REG_* defines

Use the AMCC_OP_REG_* register offset defines for the magic numbers
used to read the nvram data.

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