net: hsr: check for return value of skb_put_padto()

skb_put_padto() can fail. So check for return type and return NULL
for skb. Caller checks for skb and acts correctly if it is NULL.

Fixes: 6d6148bc ("net: hsr: fix incorrect lsdu size in the tag of HSR frames for small frames")

Signed-off-by: Murali Karicheri <m-karicheri2@ti.com>
Signed-off-by: David S. Miller <davem@davemloft.net>