fix doxygen brief in subzero header files

src/IceRegAlloc.h

Index: src/IceRegAlloc.h
diff --git a/src/IceRegAlloc.h b/src/IceRegAlloc.h
index 8faacc7e3e4d0448a4ce84f40eed9f5cc60a6789..2776f5b86c06e90b24be91d63d577dec54711eda 100644
--- a/src/IceRegAlloc.h
+++ b/src/IceRegAlloc.h
@@ -8,9 +8,10 @@
 //===----------------------------------------------------------------------===//
 ///
 /// \file
-/// This file declares the LinearScan data structure used during linear-scan
-/// register allocation, which holds the various work queues for the linear-scan
-/// algorithm.
+/// \brief Declares the LinearScan data structure used during linear-scan
+/// register allocation.
+///
+/// This holds the various work queues for the linear-scan algorithm.
 ///
 //===----------------------------------------------------------------------===//