net/hsr: Check skb_put_padto() return value

skb_put_padto() will free the sk_buff passed as reference in case of
errors, but we still need to check its return value and decide what to
do.

Detected by CoverityScan, CID#1416688 ("CHECKED_RETURN")

Fixes: ee1c2797 ("net/hsr: Added support for HSR v1")
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>