Fix FP32 TensorRT model export (ultralytics#8046)

Fixed FP32 TRT  model export

Co-authored-by: Glenn Jocher <glenn.jocher@ultralytics.com>

export.py

@@ -268,8 +268,8 @@ def export_engine(model, im, file, train, half, simplify, workspace=4, verbose=F
         for out in outputs:
             LOGGER.info(f'{prefix}\toutput "{out.name}" with shape {out.shape} and dtype {out.dtype}')
 
-        LOGGER.info(f'{prefix} building FP{16 if builder.platform_has_fast_fp16 else 32} engine in {f}')
-        if builder.platform_has_fast_fp16:
+        LOGGER.info(f'{prefix} building FP{16 if builder.platform_has_fast_fp16 and half else 32} engine in {f}')
+        if builder.platform_has_fast_fp16 and half:
             config.set_flag(trt.BuilderFlag.FP16)
         with builder.build_engine(network, config) as engine, open(f, 'wb') as t:
             t.write(engine.serialize())