LU-15601 osd-ldiskfs: handle read_inode_bitmap() error

LU-15601 osd-ldiskfs: handle read_inode_bitmap() error

Correctly handle a PTR_ERR() error return from read_inode_bitmap().
This changed in upstream kernel commit v4.3-rc2-17-g9008a58e5dce,
so handle this for both types of return value.

Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Change-Id: I184c09b300ed69c29e4a7ef343f473b67080381f
Reviewed-on: https://review.whamcloud.com/46660
Tested-by: jenkins <devops@whamcloud.com>
Reviewed-by: Yang Sheng <ys@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>