net: hsr: prevent NULL pointer dereference in hsr_proxy_announce()

In the function hsr_proxy_annouance() added in the previous commit
5f703ce5 ("net: hsr: Send supervisory frames to HSR network
with ProxyNodeTable data"), the return value of the hsr_port_get_hsr()
function is not checked to be a NULL pointer, which causes a NULL
pointer dereference.

To solve this, we need to add code to check whether the return value
of hsr_port_get_hsr() is NULL.

Reported-by:  <syzbot+02a42d9b1bd395cbcab4@syzkaller.appspotmail.com>
Fixes: 5f703ce5 ("net: hsr: Send supervisory frames to HSR network with ProxyNodeTable data")
Signed-off-by: Jeongjun Park <aha310510@gmail.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Acked-by: Lukasz Majewski <lukma@denx.de>
Link: https://patch.msgid.link/20240907190341.162289-1-aha310510@gmail.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>