RDMA/nldev: Prevent underflow in nldev_stat_set_counter_dynamic_doit()

This code checks "index" for an upper bound but it does not check for
negatives.  Change the type to unsigned to prevent underflows.

Fixes: 3c3c1f14 ("RDMA/nldev: Allow optional-counter status configuration through RDMA netlink")
Link: https://lore.kernel.org/r/20220316083948.GC30941@kiliSigned-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>

drivers/infiniband/core/nldev.c

@@ -1951,9 +1951,10 @@ static int nldev_stat_set_counter_dynamic_doit(struct nlattr *tb[],
 					       u32 port)
 {
 	struct rdma_hw_stats *stats;
-	int rem, i, index, ret = 0;
 	struct nlattr *entry_attr;
 	unsigned long *target;
+	int rem, i, ret = 0;
+	u32 index;
 
 	stats = ib_get_hw_stats_port(device, port);
 	if (!stats)