hexagon: update reference, kerneltrap.org no longer works

kerneltrap.org no longer works, update to a working reference
Signed-off-by: NPranith Kumar <bobby.prani@gmail.com>
Acked-by: NRichard Kuo <rkuo@codeaurora.org>
Signed-off-by: NJiri Kosina <jkosina@suse.cz>

arch/hexagon/include/asm/cache.h

@@ -28,7 +28,7 @@
 #define __cacheline_aligned	__aligned(L1_CACHE_BYTES)
 #define ____cacheline_aligned	__aligned(L1_CACHE_BYTES)
 
-/* See http://kerneltrap.org/node/15100  */
+/* See http://lwn.net/Articles/262554/ */
 #define __read_mostly
 
 #endif