[ATM]: Suppress some sparse warnings

  CHECK   net/atm/br2684.c
net/atm/br2684.c:665:13: warning: context imbalance in 'br2684_seq_start' - wrong count at exit
net/atm/br2684.c:676:13: warning: context imbalance in 'br2684_seq_stop' - unexpected unlock
  CHECK   net/atm/lec.c
net/atm/lec.c:196:23: warning: expensive signed divide
  CHECK   net/atm/proc.c
net/atm/proc.c:151:14: warning: context imbalance in 'vcc_seq_start' - wrong count at exit
net/atm/proc.c:154:13: warning: context imbalance in 'vcc_seq_stop' - unexpected unlock

Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>
Signed-off-by: David S. Miller <davem@davemloft.net>