ceph: don't SetPageError on readpage errors

PageError really only has meaning within a particular subsystem. Nothing
looks at this bit in the core kernel code, and ceph itself doesn't care
about it. Don't bother setting the PageError bit on error.

Signed-off-by: Jeff Layton <jlayton@kernel.org>
Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>