Replace a (1.0f / 2.0f) with 0.5f

I tried to replace all of them during code review, but missed one.

No behavior change.

Bug: none
Change-Id: Ifc487d9b86eab19e9b3cb015e05d61fe38816017
Reviewed-on: https://pdfium-review.googlesource.com/c/pdfium/+/131991
Reviewed-by: Nico Weber <thakis@google.com>
Auto-Submit: Nico Weber <thakis@chromium.org>
Reviewed-by: Lei Zhang <thestig@chromium.org>
Commit-Queue: Lei Zhang <thestig@chromium.org>
diff --git a/core/fpdfapi/render/cpdf_rendershading.cpp b/core/fpdfapi/render/cpdf_rendershading.cpp
index 501d900..e983683 100644
--- a/core/fpdfapi/render/cpdf_rendershading.cpp
+++ b/core/fpdfapi/render/cpdf_rendershading.cpp
@@ -595,7 +595,7 @@
       };
       std::array<CFX_PointF, 2> level2 = {
           0.5f * (level1[0] + level1[1]),
-          (1.0f / 2.0f) * (level1[1] + level1[2]),
+          0.5f * (level1[1] + level1[2]),
       };
       CFX_PointF level3 = 0.5f * (level2[0] + level2[1]);