ceph_osdc_readpages() returns number of bytes read, currently,
the code only allocate full-zero page into fscache, this patch
fixes this.
Signed-off-by: NLi Wang <liwang@ubuntukylin.com>
Reviewed-by: NMilosz Tanski <milosz@adfin.com>
Reviewed-by: NSage Weil <sage@inktank.com>