kfifo: fix kerneldoc for kfifo_avail and kfifo_in_locked

Function argument is not having "len" anywhere;
"len" is later used in kfifo_{in|out}.

So here, it would be appropriate to say,
it copies @n bytes and not @len
Signed-off-by: Viral Mehta <viral.mehta@lntinfotech.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

include/linux/kfifo.h

@@ -202,7 +202,7 @@ static inline __must_check unsigned int kfifo_avail(struct kfifo *fifo)
  * @n: the length of the data to be added.
  * @lock: pointer to the spinlock to use for locking.
  *
- * This function copies at most @len bytes from the @from buffer into
+ * This function copies at most @n bytes from the @from buffer into
  * the FIFO depending on the free space, and returns the number of
  * bytes copied.
  */
@@ -228,7 +228,7 @@ static inline unsigned int kfifo_in_locked(struct kfifo *fifo,
  * @n: the size of the destination buffer.
  * @lock: pointer to the spinlock to use for locking.
  *
- * This function copies at most @len bytes from the FIFO into the
+ * This function copies at most @n bytes from the FIFO into the
  * @to buffer and returns the number of copied bytes.
  */
 static inline __must_check unsigned int kfifo_out_locked(struct kfifo *fifo,