libceph: rename parse_fsid() to ceph_parse_fsid() and export

... as it is too generic. also, use __func__ when logging
rather than hardcoding the function name.

Signed-off-by: Venky Shankar <vshankar@redhat.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>