x86, cleanup: fix description of __fls(): __fls(0) is undefined

Ricardo M. Correia spotted that the use of __fls() in fls64() did
not seem to make sense. In fact fls64()'s implementation is fine,
but the description of __fls() was wrong. Fix that.
Reported-by: N"Ricardo M. Correia" <Ricardo.M.Correia@Sun.COM>
Signed-off-by: NAlexander van Heukelum <heukelum@fastmail.fm>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andi Kleen <andi@firstfloor.org>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

include/asm-x86/bitops.h

@@ -356,7 +356,7 @@ static inline unsigned long ffz(unsigned long word)
  * __fls: find last set bit in word
  * @word: The word to search
  *
- * Undefined if no zero exists, so code should check against ~0UL first.
+ * Undefined if no set bit exists, so code should check against 0 first.
  */
 static inline unsigned long __fls(unsigned long word)
 {