Fix --define xnnpack_force_float_precision=fp16 in XNNPACK delegate

PiperOrigin-RevId: 429215341
Change-Id: Ia85e918cd9f32fee341fdbc9e70574583053fbc8
diff --git a/tensorflow/lite/delegates/xnnpack/BUILD b/tensorflow/lite/delegates/xnnpack/BUILD
index 8c43bcf..1aebfdb 100644
--- a/tensorflow/lite/delegates/xnnpack/BUILD
+++ b/tensorflow/lite/delegates/xnnpack/BUILD
@@ -110,7 +110,7 @@
     hdrs = ["xnnpack_delegate.h"],
     compatible_with = get_compatible_with_portable(),
     copts = tflite_copts() + select({
-        ":xnnpack_force_float_precision_explicit_fp16": ["XNNPACK_DELEGATE_FORCE_PRECISION_FP16=1"],
+        ":xnnpack_force_float_precision_explicit_fp16": ["-DXNNPACK_DELEGATE_FORCE_PRECISION_FP16=1"],
         "//conditions:default": [],
     }),
     linkstatic = True,