rose: Fix signedness issues wrt. digi count.

Just use explicit casts, since we really can't change the
types of structures exported to userspace which have been
around for 15 years or so.

Reported-by: Dan Rosenberg <dan.j.rosenberg@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/rose/af_rose.c b/net/rose/af_rose.c
index 8e45e76..d952e7e 100644
--- a/net/rose/af_rose.c
+++ b/net/rose/af_rose.c
@@ -679,7 +679,7 @@
 	if (addr_len == sizeof(struct sockaddr_rose) && addr->srose_ndigis > 1)
 		return -EINVAL;
 
-	if (addr->srose_ndigis > ROSE_MAX_DIGIS)
+	if ((unsigned int) addr->srose_ndigis > ROSE_MAX_DIGIS)
 		return -EINVAL;
 
 	if ((dev = rose_dev_get(&addr->srose_addr)) == NULL) {
@@ -739,7 +739,7 @@
 	if (addr_len == sizeof(struct sockaddr_rose) && addr->srose_ndigis > 1)
 		return -EINVAL;
 
-	if (addr->srose_ndigis > ROSE_MAX_DIGIS)
+	if ((unsigned int) addr->srose_ndigis > ROSE_MAX_DIGIS)
 		return -EINVAL;
 
 	/* Source + Destination digis should not exceed ROSE_MAX_DIGIS */