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/DrmProperty.cpp b/drm/DrmProperty.cpp
index dbd307e..76fb4f9 100644
--- a/drm/DrmProperty.cpp
+++ b/drm/DrmProperty.cpp
@@ -144,4 +144,19 @@
   return {};
 }
 
+auto DrmProperty::GetEnumMask(uint64_t &mask) -> bool {
+  if (enums_.empty()) {
+    ALOGE("No enum values for property: %s", name_.c_str());
+    return false;
+  }
+
+  mask = 0;
+
+  for (const auto &it : enums_) {
+    mask |= it.value;
+  }
+
+  return true;
+}
+
 }  // namespace android