apply fp16 autocast only to floating point values

deepspeed/runtime/engine.py

@@ -1928,7 +1928,7 @@ def _cast_inputs_half(self, inputs):
             for k, v in inputs.items():
                 new_inputs[k] = self._cast_inputs_half(v)
             return new_inputs
-        elif hasattr(inputs, 'half'):
+        elif hasattr(inputs, 'half') and inputs.is_floating_point():
             return inputs.half()
         else:
             return inputs