No, there should not be a shot clock. Just because a team is not shooting does not mean the team is wasting time. In soccer, there is a difference between wasting time and using time.
Time wasting is illegal. Time wasting usually involves delaying the restart of play. An example is if a team is leading near the end of the match, and is awarded a throw in. If a player picks up the ball and prepares to throw it, but then calls for a distant teammate to take it instead, that's delaying the start of play. A yellow card is in order, and the referee should add the time lost as stoppage time.
On the other hand, using time is perfectly legal, and is a common strategy. An example is when a team with the lead starts to play keep away. Just because they are not trying to score does not create a violation. The possession passes are designed to prevent the opponents from getting chances to catch up.
