tools: kwboot: Fix comparison of integers with different size

The compiler complains that we are comparing int with size_t when
compiled with -W.

Signed-off-by: Marek BehĂșn <marek.behun@nic.cz>
Reviewed-by: Stefan Roese <sr@denx.de>
diff --git a/tools/kwboot.c b/tools/kwboot.c
index 88353d1..3d9f73e 100644
--- a/tools/kwboot.c
+++ b/tools/kwboot.c
@@ -352,8 +352,7 @@
 		    size_t size, int pnum)
 {
 	const size_t blksz = sizeof(block->data);
-	size_t n;
-	int i;
+	size_t i, n;
 
 	block->soh = SOH;
 	block->pnum = pnum;