drivers/isdn/capi: fix sparse warning: context imbalance

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

Fix this sparse warnings:
  drivers/isdn/capi/kcapi_proc.c:241:13: warning: context imbalance in 'capi_driver_start' - wrong count at exit
  drivers/isdn/capi/kcapi_proc.c:252:13: warning: context imbalance in 'capi_driver_stop' - unexpected unlock

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

drivers/isdn/capi/kcapi_proc.c

@@ -239,6 +239,7 @@ static const struct file_operations proc_applstats_ops = {
 // ---------------------------------------------------------------------------
 
 static void *capi_driver_start(struct seq_file *seq, loff_t *pos)
+	__acquires(&capi_drivers_list_lock)
 {
 	read_lock(&capi_drivers_list_lock);
 	return seq_list_start(&capi_drivers, *pos);
@@ -250,6 +251,7 @@ static void *capi_driver_next(struct seq_file *seq, void *v, loff_t *pos)
 }
 
 static void capi_driver_stop(struct seq_file *seq, void *v)
+	__releases(&capi_drivers_list_lock)
 {
 	read_unlock(&capi_drivers_list_lock);
 }