vfs: Fix vmtruncate() regression

If __block_prepare_write() was failed in block_write_begin(), the
allocated blocks can be outside of ->i_size.

But new truncate_pagecache() in vmtuncate() does nothing if new < old.
It means the above usage is not working anymore.

So, this patch fixes it by removing "new < old" check. It would need
more cleanup/change. But, now -rc and truncate working is in progress,
so, this tried to fix it minimum change.
Acked-by: Nick Piggin <npiggin@suse.de>
Signed-off-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/truncate.c

@@ -522,7 +522,6 @@ EXPORT_SYMBOL_GPL(invalidate_inode_pages2);
  */
 void truncate_pagecache(struct inode *inode, loff_t old, loff_t new)
 {
-	if (new < old) {
 	struct address_space *mapping = inode->i_mapping;
 
 	/*
@@ -537,7 +536,6 @@ void truncate_pagecache(struct inode *inode, loff_t old, loff_t new)
 	unmap_mapping_range(mapping, new + PAGE_SIZE - 1, 0, 1);
 	truncate_inode_pages(mapping, new);
 	unmap_mapping_range(mapping, new + PAGE_SIZE - 1, 0, 1);
-	}
 }
 EXPORT_SYMBOL(truncate_pagecache);