usrp1: Update device API for frequency offset tuning
usrp1: Update device API for frequency offset tuning

Commit 8e17df7374367d57 "Add option for baseband frequency offset",
modified the base device API to allow for RF tuning, which was never
updated for the USRP1.

Update the implementation to match the API, however, note actual offset
in the USRP1 remains unsupported.

Signed-off-by: Tom Tsou <96835dd8bfa718bd6447ccc87af89ae1675daeca@tsou.cc>

osmocom/osmo-trx,kkroo/osmo-trx,kkroo/osmo-trx,ttsou/osmo-trx,kkroo/osmo-trx,ttsou/osmo-trx,osmocom/osmo-trx,pothosware/osmo-trx,pothosware/osmo-trx,kkroo/osmo-trx,pothosware/osmo-trx,ttsou/osmo-trx,pothosware/osmo-trx,osmocom/osmo-trx,osmocom/osmo-trx,ttsou/osmo-trx