dm dust: remove redundant unsigned comparison to less than zero

Variable block is an unsigned long long hence the less than zero
comparison is always false, hence it is redundant and can be removed.

Addresses-Coverity: ("Unsigned compared against 0")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Reviewed-by: Bryan Gurney <bgurney@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

drivers/md/dm-dust.c

@@ -411,7 +411,7 @@ static int dust_message(struct dm_target *ti, unsigned int argc, char **argv,
 
 		block = tmp;
 		sector_div(size, dd->sect_per_block);
-		if (block > size || block < 0) {
+		if (block > size) {
 			DMERR("selected block value out of range");
 			return result;
 		}