osmo-bts-trx/scheduler: fix: check rc of osmo_ecu_frame_out()
osmo-bts-trx/scheduler: fix: check rc of osmo_ecu_frame_out()

Change-Id: I32d244f5ddef46c8b8719f5ec27b7456514d407a
Fixes: CID#204005 (CID#204007), CID#204006 (CID#204004)

osmocom/osmo-bts,osmocom/osmo-bts,osmocom/osmo-bts