arch/tile: revert comment for atomic64_add_unless().

It still returns whether @v was not @u, not the old value,
unlike __atomic_add_unless().

Signed-off-by: Chris Metcalf <[e-mail]>
Acked-by: Arun Sharma <[e-mail]>

arch/tile/include/asm/atomic_32.h

···
  * @u: ...unless v is equal to u.
  *
  * Atomically adds @a to @v, so long as @v was not already @u.
- * Returns the old value of @v.
+ * Returns non-zero if @v was not @u, and zero otherwise.
  */
 static inline u64 atomic64_add_unless(atomic64_t *v, u64 a, u64 u)
 {