devlink: fix memory leak on 'resource'

Currently, if the call to devlink_resource_find returns null then
the error exit path does not free the devlink_resource 'resource'
and a memory leak occurs. Fix this by kfree'ing resource on the
error exit path.

Detected by CoverityScan, CID#1464184 ("Resource leak")

Fixes: d9f9b9a4

 ("devlink: Add support for resource abstraction")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Acked-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>