uhd: Fix UmTRX tuning broken in commit 90f7a01d.
uhd: Fix UmTRX tuning broken in commit 90f7a01d.

Commit 90f7a01d lost "return" statement. We also should account the fact that
offset can be negative.
We should return the tuning request immediately after

Signed-off-by: Tom Tsou <072b11b861b7a066437a0a0cead1208995732a66@ettus.com>

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