[Blackfin] arch: Clean up the definition and correct the commentary for current_thread_info().

Signed-off-by: Robert P. J. Day <rpjday@crashcourse.ca>
Acked-by: Mike Frysinger <vapier.adi@gmail.com>
Signed-off-by: Bryan Wu <cooloney@kernel.org>

include/asm-blackfin/thread_info.h

@@ -81,14 +81,11 @@ struct thread_info {
 #define init_thread_info	(init_thread_union.thread_info)
 #define init_stack		(init_thread_union.stack)
 
-/* How to get the thread information struct from C */
-
-static inline struct thread_info *current_thread_info(void)
-    __attribute__ ((__const__));
-
-/* Given a task stack pointer, you can find it's task structure
- * just by masking it to the 8K boundary.
+/* Given a task stack pointer, you can find its corresponding
+ * thread_info structure just by masking it to the THREAD_SIZE
+ * boundary (currently 8K as you can see above).
  */
+__attribute_const__
 static inline struct thread_info *current_thread_info(void)
 {
 	struct thread_info *ti;