ceph: Fix __ceph_do_pending_vmtruncate

we should set i_truncate_pending to 0 after page cache is truncated
to i_truncate_size

Signed-off-by: Yan, Zheng <zheng.z.yan@intel.com>
Signed-off-by: Sage Weil <sage@inktank.com>
(cherry picked from commit a85f50b6ef93fbbb2ae932ce9b2376509d172796)
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>