selftests: nci: replace unsigned int with int

Should not use comparison of unsigned expressions < 0.

Signed-off-by: Xiang wangx <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

tools/testing/selftests/nci/nci_dev.c

···
 		       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);