net/wan/hdlc_ppp: use break in switch

We'll either hit one of the case labels or the default in the switch
and in all cases do we then 'goto out' and we also have a 'goto out'
after the switch that is redundant. Change to just use break in the
case statements and leave the 'goto out' after the lop for everyone to
hit.

Signed-off-by: Jesper Juhl <jj@chaosbits.net>
Signed-off-by: David S. Miller <davem@davemloft.net>