fuse: Convert fuse_readpages_end() to use folio_end_read()

Nobody checks the error flag on fuse folios, so stop setting it.
Optimise the (optional) setting of the uptodate flag and clearing
of the lock flag by using folio_end_read().

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>