of: return -ENOENT when no property

Make of_parse_phandle_with_args return -ENOENT instead of -EINVAL when
no matching property is found, which allows to discriminate between
absence of property and parsing error.

Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>
Signed-off-by: Rob Herring <rob.herring@calxeda.com>