fs: fix buffer invalidation in invalidate_list

fs: fix buffer invalidation in invalidate_list

We must not call invalidate_inode_buffers in invalidate_list unless the
inode can be reclaimed.  If we remove the buffer association of a busy
inode fsync won't find the buffers anymore.  As invalidate_inode_buffers
is called from various others sources than umount this actually does
matter in practice.

While at it change the loop to a more natural form and remove the
WARN_ON for I_NEW, wich we already tested a few lines above.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>