doxygen: Fix all the "\returns" so they work as part of complete sentences.

include/SDL_bits.h

@@ -45,7 +45,7 @@ extern "C" {
  *  with 0. This operation can also be stated as "count leading zeroes" and
  *  "log base 2".
  *
- *  \return Index of the most significant bit, or -1 if the value is 0.
+ *  \return the index of the most significant bit, or -1 if the value is 0.
  */
 #if defined(__WATCOMC__) && defined(__386__)
 extern _inline int _SDL_bsr_watcom (Uint32);