selftests: nci: replace unsigned int with int

Should not use comparison of unsigned expressions < 0.
Signed-off-by: Xiang wangx <wangxiang@cdjrlc.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

tools/testing/selftests/nci/nci_dev.c

@@ -746,7 +746,7 @@ int read_write_nci_cmd(int nfc_sock, int virtual_fd, const __u8 *cmd, __u32 cmd_
 		       const __u8 *rsp, __u32 rsp_len)
 {
 	char buf[256];
-	unsigned int len;
+	int len;
 
 	send(nfc_sock, &cmd[3], cmd_len - 3, 0);
 	len = read(virtual_fd, buf, cmd_len);