Patch from Nikita Danilov <Nikita@Namesys.COM>

read_cache_pages() is passed a bunch of pages to start I/O against and it is
supposed to consume all those pages.  But if there is an I/O error, someone
need to throw away the unused pages.

At present the single user of read_cache_pages() (nfs_readpages) does that
cleanup by hand.  But it should be done in the core kernel.