counter: fix an IS_ERR() vs NULL bug

There are 8 callers for devm_counter_alloc() and they all check for NULL
instead of error pointers. I think NULL is the better thing to return
for allocation functions so update counter_alloc() and devm_counter_alloc()
to return NULL instead of error pointers.

Fixes: c18e2760308e ("counter: Provide alternative counter registration functions")
Acked-by: Uwe Kleine-König <[e-mail]>
Acked-by: William Breathitt Gray <[e-mail]>
Signed-off-by: Dan Carpenter <[e-mail]>
Link: https://lore.kernel.org/r/20220111173243.GA2192@kili
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/counter/counter-core.c

···
 	int err;
 
 	ch = kzalloc(sizeof(*ch) + sizeof_priv, GFP_KERNEL);
-	if (!ch) {
-		err = -ENOMEM;
-		goto err_alloc_ch;
-	}
+	if (!ch)
+		return NULL;
 
 	counter = &ch->counter;
 	dev = &counter->dev;
···
 err_ida_alloc:
 
 	kfree(ch);
-err_alloc_ch:
 
-	return ERR_PTR(err);
+	return NULL;
 }
 EXPORT_SYMBOL_GPL(counter_alloc);
 
···
 	int err;
 
 	counter = counter_alloc(sizeof_priv);
-	if (IS_ERR(counter))
-		return counter;
+	if (!counter)
+		return NULL;
 
 	err = devm_add_action_or_reset(dev, devm_counter_put, counter);
 	if (err < 0)
-		return ERR_PTR(err);
+		return NULL;
 
 	return counter;
 }