Fix a logic error in examples/ioctl.c (#137)

Change the "alloc_ret" and "cdev_ret" initial values to non-zero.
According to the source code, "alloc_chrdev_region" and "cdev_add"
return zero on success, and negative code on failure.

So, if the "alloc_chrdev_region" failed, the if condition becomes true,
then we will jump to the label "error" by goto, checking each return
value whether is a success state from both functions mentioned above
and dealing with it properly for exiting the process.

However, it checks the success state by comparing the return value
with zero (means success), and we got "cdev_ret == 0" is true from
the initial value zero, while we didn't execute "cdev_add" yet.
Hence, there was a logic error when the initial value is zero.

Co-authored-by: NOVBobLee <[email protected]>

Author: NOVBobLee

examples/ioctl.c

@@ -149,8 +149,8 @@ static struct file_operations fops = {
 static int ioctl_init(void)
 {
     dev_t dev;
-    int alloc_ret = 0;
-    int cdev_ret = 0;
+    int alloc_ret = -1;
+    int cdev_ret = -1;
     alloc_ret = alloc_chrdev_region(&dev, 0, num_of_dev, DRIVER_NAME);
 
     if (alloc_ret)