sysmo: l1if_mute_rf: Declare vars inside ifdef section
sysmo: l1if_mute_rf: Declare vars inside ifdef section

Otherwise sysp variable is unused and compiler triggers a warn.

Change-Id: Ie3a3529442a36bb885ef634b8b49ac801bd263da

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