MIPS: atomic: Fix comment describing atomic64_add_unless's return value.

Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
Fixes: f24219b4e9
(cherry picked from commit f0a232cde7be18a207fd057dd79bbac8a0a45dec)

arch/mips/include/asm/atomic.h

@@ -507,7 +507,7 @@ static __inline__ long atomic64_sub_if_positive(long i, atomic64_t * v)
  * @u: ...unless v is equal to u.
  *
  * Atomically adds @a to @v, so long as it was not @u.
- * Returns the old value of @v.
+ * Returns true iff @v was not @u.
  */
 static __inline__ int atomic64_add_unless(atomic64_t *v, long a, long u)
 {