devlink: Compare to size_new in case of resource child validation

The current implementation checks the combined size of the children with
the 'size' of the parent. The correct behavior is to check the combined
size vs the pending change and to compare vs the 'size_new'.

Fixes: d9f9b9a4 ("devlink: Add support for resource abstraction")
Signed-off-by: Arkadi Sharshevsky <arkadis@mellanox.com>
Tested-by: Yuval Mintz <yuvalm@mellanox.com>
Signed-off-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>