dsa: fix warning in net/dsa/mv88e6060.c

this warning:

  net/dsa/mv88e6060.c: In function ‘mv88e6060_poll_link’:
  net/dsa/mv88e6060.c:225: warning: ‘port_status’ may be used uninitialized in this function

triggers because GCC does not recognize the (correct) error flow
between 'link' and 'port_status'.

Annotate it.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: David S. Miller <davem@davemloft.net>