A screwdriver can be used as a chisel and I've done so many times myself.
Although be aware that you can get hurt using a screwdriver as a chisel if you're not careful because the plastic handle could break off the screwdriver as you're pounding the screwdriver with a hammer.
However gently hammering the top of the screwdriver can safely work as a chisel.
I actually have an older screwdriver that has a metal piece to the top of it where you can use a hammer to hit it so it is designed to be used as both a screwdriver and a chisel safely.
I would recommend though getting a good chisel to prevent damage to your screwdrivers though a good chisel can be bought pretty cheap.