LU-13030 pcc: Init saved dataset flags properly

When init a new inode, the saved flags is set wrongly with
PCC_DATASET_NONE which means that the file is known in NONE
of PCC dataset.
This patch corrects it with PCC_DATASET_INVALID.

Signed-off-by: Qian Yingjin <qian@ddn.com>
Change-Id: Id775a20711cbc89979e81cbb2b0fe77dc5a850d5
Reviewed-on: https://review.whamcloud.com/36923
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Li Xi <lixi@ddn.com>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>