e1000/e1000e/igb/igbvf/ixgb/ixgbe: Fix tests of unsigned in *_tx_map()

The variable count and i are unsigned so the (<|>=)0 tests do not work.

Signed-off-by: Roel Kluin <roel.kluin@gmail.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/net/igbvf/netdev.c b/drivers/net/igbvf/netdev.c
index 0dbd032..10e038a 100644
--- a/drivers/net/igbvf/netdev.c
+++ b/drivers/net/igbvf/netdev.c
@@ -2163,14 +2163,14 @@
 	buffer_info->length = 0;
 	buffer_info->next_to_watch = 0;
 	buffer_info->mapped_as_page = false;
-	count--;
+	if (count)
+		count--;
 
 	/* clear timestamp and dma mappings for remaining portion of packet */
-	while (count >= 0) {
-		count--;
-		i--;
-		if (i < 0)
+	while (count--) {
+		if (i==0)
 			i += tx_ring->count;
+		i--;
 		buffer_info = &tx_ring->buffer_info[i];
 		igbvf_put_txbuf(adapter, buffer_info);
 	}