service: fix parameter type for attribute

service: fix parameter type for attribute

The type of value parameter to rte_service_attr_get
should be uint64_t *, since the attributes
are of type uint64_t.

Fixes: 4d55194d76a4 ("service: add attribute get function")

Signed-off-by: Nikhil Rao <nikhil.rao@intel.com>
Reviewed-by: Gage Eads <gage.eads@intel.com>
Reviewed-by: Rami Rosen <ramirose@gmail.com>
Acked-by: Harry van Haaren <harry.van.haaren@intel.com>