Btrfs: Use invalidatepage when writepage finds a page outside of i_size

With all the recent fixes to the delalloc locking, it is now safe
again to use invalidatepage inside the writepage code for
pages outside of i_size.  This used to deadlock against some of the
code to write locked ranges of pages, but all of that has been fixed.

Signed-off-by: Chris Mason <chris.mason@oracle.com>
diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index 69ea096..af2d9a9 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -2174,11 +2174,7 @@
 	pg_offset = i_size & (PAGE_CACHE_SIZE - 1);
 	if (page->index > end_index ||
 	   (page->index == end_index && !pg_offset)) {
-		if (epd->extent_locked) {
-			if (tree->ops && tree->ops->writepage_end_io_hook)
-				tree->ops->writepage_end_io_hook(page, start,
-							 page_end, NULL, 1);
-		}
+		page->mapping->a_ops->invalidatepage(page, 0);
 		unlock_page(page);
 		return 0;
 	}