Btrfs: adjust NULL test

Move the call to BUG_ON to before the dereference of the tested value.

Signed-off-by: Julia Lawall <julia@diku.dk>
Signed-off-by: Chris Mason <chris.mason@oracle.com>
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index a48c084..3ea827d 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -2607,8 +2607,8 @@
 	if (root->ref_cows)
 		btrfs_drop_extent_cache(inode, new_size & (~mask), (u64)-1, 0);
 	path = btrfs_alloc_path();
-	path->reada = -1;
 	BUG_ON(!path);
+	path->reada = -1;
 
 	/* FIXME, add redo link to tree so we don't leak on crash */
 	key.objectid = inode->i_ino;