ceph: Correctly return NXIO errors from ceph_llseek

ceph: Correctly return NXIO errors from ceph_llseek

commit 955818cd5b6c4b58ea574ace4573e7afa4c19c1e upstream.

ceph_llseek does not correctly return NXIO errors because the 'out' path
always returns 'offset'.

Fixes: 06222e491e66 ("fs: handle SEEK_HOLE/SEEK_DATA properly in all fs's that define their own llseek")
Signed-off-by: Phil Turnbull <phil.turnbull@oracle.com>
Signed-off-by: Yan, Zheng <zyan@redhat.com>
[bwh: Backported to 3.2:
 - We don't use vfs_setpos(); instead set ret = -EINVAL or ret = offset
   directly
 - Adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>