staging: speakup: Replace BUG_ON() with WARN_ON().

BUG_ON() is replaced with WARN_ON() and EINVAL is returned, when
WARN_ON() is true. This fixes the following checkpatch issue:

Avoid crashing the kernel - try using WARN_ON & recovery code rather
than BUG() or BUG_ON().
Signed-off-by: Varsha Rao <rvarsha016@gmail.com>
Reviewed-by: Samuel Thibault <samuel.thibault@ens-lyon.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/speakup/kobjects.c

@@ -833,7 +833,9 @@ static ssize_t message_show(struct kobject *kobj,
 	struct msg_group_t *group = spk_find_msg_group(attr->attr.name);
 	unsigned long flags;
 
-	BUG_ON(!group);
+	if (WARN_ON(!group))
+		return -EINVAL;
+
 	spin_lock_irqsave(&speakup_info.spinlock, flags);
 	retval = message_show_helper(buf, group->start, group->end);
 	spin_unlock_irqrestore(&speakup_info.spinlock, flags);
@@ -845,7 +847,9 @@ static ssize_t message_store(struct kobject *kobj, struct kobj_attribute *attr,
 {
 	struct msg_group_t *group = spk_find_msg_group(attr->attr.name);
 
-	BUG_ON(!group);
+	if (WARN_ON(!group))
+		return -EINVAL;
+
 	return message_store_helper(buf, count, group);
 }