btrfs: Use WARN_ON()'s return value in place of WARN_ON(1)

Use WARN_ON()'s return value in place of WARN_ON(1) for cleaner source
code that outputs a more descriptive warnings. Also fix the styling
warning of redundant braces that came up as a result of this fix.

Signed-off-by: Dulshani Gunawardhana <dulshani.gunawardhana89@gmail.com>
Reviewed-by: Zach Brown <zab@redhat.com>
Signed-off-by: Josef Bacik <jbacik@fusionio.com>
Signed-off-by: Chris Mason <chris.mason@fusionio.com>
diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index a93bab4..fb782ed 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -1739,10 +1739,8 @@
 	u64 last = 0;
 	int found = 0;
 
-	if (search_end <= cur_start) {
-		WARN_ON(1);
+	if (WARN_ON(search_end <= cur_start))
 		return 0;
-	}
 
 	spin_lock(&tree->lock);
 	if (cur_start == 0 && bits == EXTENT_DIRTY) {
@@ -3568,9 +3566,8 @@
 			 * but no sense in crashing the users box for something
 			 * we can survive anyway.
 			 */
-			if (!eb) {
+			if (WARN_ON(!eb)) {
 				spin_unlock(&mapping->private_lock);
-				WARN_ON(1);
 				continue;
 			}