[PATCH] bonding: fix ->get_settings error checking

Since get_settings() returns a signed int and it gets checked
for < 0 to catch an error, res should be a signed int too.

Signed-off-by: Eric Sesterhenn <snakebyte@gmx.de>
Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: Jeff Garzik <jgarzik@pobox.com>