common/rsl.c: fix NULL-pointer dereference in rsl_rx_rll()
common/rsl.c: fix NULL-pointer dereference in rsl_rx_rll()

Change-Id: I07e39e69a42dd09841f5d03608ec0d0b2345139a
Fixes: CID#198663 Null pointer dereferences

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