drm_hwcomposer: Simplify LayerTransform

Fixes clang-analyzer-optin.core.EnumCastOutOfRange clang tidy check.

Change-Id: I0a88d1ef084848c924198e8bd3831533b6578675
Signed-off-by: Roman Stratiienko <r.stratiienko@gmail.com>
diff --git a/drm/DrmPlane.h b/drm/DrmPlane.h
index c26a3cc..24d21c8 100644
--- a/drm/DrmPlane.h
+++ b/drm/DrmPlane.h
@@ -96,6 +96,6 @@
   std::map<BufferBlendMode, uint64_t> blending_enum_map_;
   std::map<BufferColorSpace, uint64_t> color_encoding_enum_map_;
   std::map<BufferSampleRange, uint64_t> color_range_enum_map_;
-  std::map<LayerTransform, uint64_t> transform_enum_map_;
+  uint64_t transform_enum_mask_ = DRM_MODE_ROTATE_0;
 };
 }  // namespace android