Probably inefficient.

Already the Romans preferred charcoal over wood in producing lime from limestone: charcoal allows reaching markedly higher temperatures.

Please note that iron ore is not mainly reduced by coke, but rather by carbon monoxide the coke is converted into.

Another challenge is dealing with the distillation products of biomass: these are corrosive (acetic acid) and yield condensibles (tar, water).

So, in brief, you will need to dry the biomass and handle its volatiles. 

As Alfons Buekens said, charcoal from biomass has been used for coke processes in the past. For current industrial steel making processes, properties of biocharcoal might not be sufficient (e.g. concerning abrasion resistance or density). If you can adjust such parameters, it should be possible to use. The question of efficiency needs a bit more of consideration - first of all, how do you define effieciency in this context? What coke is substituted (from hard coal or brown coal)? What steel making process do you refer to?

I have used biomass to make self-reducing pellets, and in my experience  the quantity needed to reduce iron oxide to iron is very close to the quantity of coal or coke that would be needed. As Alfons Bukens says above, it is the carbon monoxide that acts as the reductant, and the cellulose in biomass converts most of its mass to carbon monoxide when it is heated. As long as the biomass is only being used as a reductant, and not also as the primary heat source (which is the other primary function of coke), it is a perfectly adequate iron oxide reductant.

raw biomass not so great.  However, going through a pretreatment step to produce torrified biomass provides a product more similar to coal while harsher pretreatment to produce biochar further eliminates issues with corrosive by-products.  However, biochar is typically powder or a highly friable solid so the problem becomes producing a suitable agglomerate such as a durable briquette or pellet.  Further, production costs are high and a significant portion of the biomass is lost during processing though the majority of the loss is as water and CO2 with some volatile HC.