tls: rx: Fix unsigned comparison with less than zero

The return from the call to tls_rx_msg_size() is int, it can be
a negative error code, however this is being assigned to an
unsigned long variable 'sz', so making 'sz' an int.

Eliminate the following coccicheck warning:
./net/tls/tls_strp.c:211:6-8: WARNING: Unsigned expression compared with zero: sz < 0

Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Signed-off-by: Yang Li <yang.lee@linux.alibaba.com>
Link: https://lore.kernel.org/r/20220728031019.32838-1-yang.lee@linux.alibaba.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

net/tls/tls_strp.c

@@ -187,9 +187,10 @@ static int tls_strp_copyin(read_descriptor_t *desc, struct sk_buff *in_skb,
 			   unsigned int offset, size_t in_len)
 {
 	struct tls_strparser *strp = (struct tls_strparser *)desc->arg.data;
-	size_t sz, len, chunk;
 	struct sk_buff *skb;
 	skb_frag_t *frag;
+	size_t len, chunk;
+	int sz;
 
 	if (strp->msg_ready)
 		return 0;