bareudp: Fix uninitialized variable warnings.

drivers/net/bareudp.c: In function 'bareudp_xmit_skb':
drivers/net/bareudp.c:346:9: warning: 'err' may be used uninitialized in this function [-Wmaybe-uninitialized]
  346 |  return err;
      |         ^~~
drivers/net/bareudp.c: In function 'bareudp6_xmit_skb':
drivers/net/bareudp.c:407:9: warning: 'err' may be used uninitialized in this function [-Wmaybe-uninitialized]
  407 |  return err;

Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>