drm_hwcomposer: C++ coding style cleanup, no functional changes.

Apply "override" keyword and remove redundant "virtual" keyword.
Ran clang-format on all files.

Change-Id: I76730296aa8f52e555137d4b5973fa27d38f0aa6
diff --git a/nvimporter.cpp b/nvimporter.cpp
index 71b3b7f..d5c3abc 100644
--- a/nvimporter.cpp
+++ b/nvimporter.cpp
@@ -161,8 +161,8 @@
       ALOGE("Failed to close gem handle %d %d", i, ret);
     } else {
       /* Clear any duplicate gem handle as well but don't close again */
-      for(int j = i + 1; j < num_gem_handles; j++)
-        if(bo->gem_handles[j] == bo->gem_handles[i])
+      for (int j = i + 1; j < num_gem_handles; j++)
+        if (bo->gem_handles[j] == bo->gem_handles[i])
           bo->gem_handles[j] = 0;
       bo->gem_handles[i] = 0;
     }