switchdev: Fix return value of switchdev_port_fdb_dump().

This patch fixes the retun value of switchdev_port_fdb_dump() when
CONFIG_NET_SWITCHDEV is not set. This avoids getting "warning: return makes
integer from pointer without a cast [-Wint-conversion]" when building
when CONFIG_NET_SWITCHDEV is not set under several compiler versions.
This warning is due to commit d297653dd6f07afbe7e6c702a4bcd7615680002e
("rtnetlink: fdb dump: optimize by saving last interface markers").

Signed-off-by: Rami Rosen <[e-mail]>
Acked-by: Roopa Prabhu <[e-mail]>
Reported-by: Eric Dumazet <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

include/net/switchdev.h

···
 					  struct net_device *filter_dev,
 					  int *idx)
 {
-       return idx;
+       return *idx;
 }
 
 static inline bool switchdev_port_same_parent_id(struct net_device *a,