Fix read_ac_dc_relay_status

[agustiner]

read_ac_dc_relay_status has bugs:

• The docstring says its DC coupled (shorted) when the relay bit is 0, which is wrong.
• Other parts of pysmurf expect either the value 0 or 3 (0b11), but it currently returns only 0 and 1 because its reading another register.

Please again confirm that 0x08 doesn't actually do anything on the C04 cryocard, because this is how we previously read out the flux ramp coupling status for both relays on the C02, hence the value of 3, 0b11. Ref https://github.com/slaclab/smurfc/blob/C04/README.SpiRegisterMap.md.