fix: when eval only, AMP can be enabled

ppcls/engine/engine.py

@@ -98,8 +98,8 @@ class Engine(object):
         logger.info('train with paddle {} and device {}'.format(
             paddle.__version__, self.device))
 
-        # AMP training
-        self.amp = True if "AMP" in self.config and self.mode == "train" else False
+        # AMP training and evaluating
+        self.amp = "AMP" in self.config
         if self.amp and self.config["AMP"] is not None:
             self.scale_loss = self.config["AMP"].get("scale_loss", 1.0)
             self.use_dynamic_loss_scaling = self.config["AMP"].get(