net: sfp: fix sfp_bus_add_upstream() warning

When building with SFP disabled, the stub for sfp_bus_add_upstream()
missed "inline".  Add it.

Fixes: 727b3668 ("net: sfp: rework upstream interface")
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/sfp.h

@@ -563,7 +563,7 @@ static inline struct sfp_bus *sfp_bus_find_fwnode(struct fwnode_handle *fwnode)
 	return NULL;
 }
 
-static int sfp_bus_add_upstream(struct sfp_bus *bus, void *upstream,
+static inline int sfp_bus_add_upstream(struct sfp_bus *bus, void *upstream,
 				       const struct sfp_upstream_ops *ops)
 {
 	return 0;