stmmac: improve/review and fix kernel-doc

this patch reviews/improves and adds some fixes in the code doc.
Also kernel-doc passes w/o any warnings.
Signed-off-by: Giuseppe Cavallaro <peppe.cavallaro@st.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/stmicro/stmmac/stmmac_ptp.c

@@ -174,9 +174,7 @@ static struct ptp_clock_info stmmac_ptp_clock_ops = {
 
 /**
  * stmmac_ptp_register
- *
- * @ndev: net device pointer
- *
+ * @priv: driver private structure
  * Description: this function will register the ptp clock driver
  * to kernel. It also does some house keeping work.
  */
@@ -199,9 +197,7 @@ int stmmac_ptp_register(struct stmmac_priv *priv)
 
 /**
  * stmmac_ptp_unregister
- *
- * @ndev: net device pointer
- *
+ * @priv: driver private structure
  * Description: this function will remove/unregister the ptp clock driver
  * from the kernel.
  */