rdmacg: Fixed uninitialized current resource usage

Fixed warning reported by kbuild test robot.
When reading current resource usage value, when no resources are
allocated, its possible that it can report a uninitialized value
for current resource usage.
This fix avoids it by initializing it to zero as no resource is
allocated.
Signed-off-by: Parav Pandit <pandit.parav@gmail.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

kernel/cgroup/rdma.c

@@ -518,6 +518,8 @@ static void print_rpool_values(struct seq_file *sf,
 		} else {
 			if (rpool)
 				value = rpool->resources[i].usage;
+			else
+				value = 0;
 		}
 
 		if (value == S32_MAX)