drivers/net/hamradio: fix sparse warning: context imbalance

drivers/net/hamradio: fix sparse warning: context imbalance

Impact: Attribute functions with __acquires(...) resp. __releases(...).

Fix this sparse warnings:
  drivers/net/hamradio/bpqether.c:387:13: warning: context imbalance in 'bpq_seq_start' - wrong count at exit
  drivers/net/hamradio/bpqether.c:419:13: warning: context imbalance in 'bpq_seq_stop' - unexpected unlock

Signed-off-by: Hannes Eder <hannes@hanneseder.net>
Signed-off-by: David S. Miller <davem@davemloft.net>