ceph: fix an oops in error handling in ceph_netfs_issue_op

ceph: fix an oops in error handling in ceph_netfs_issue_op

Dan reported a potential oops in the cleanup if ceph_osdc_new_request
returns an error. Eliminate the unneeded initialization of "req" and
then just set it to NULL in the case where it holds an ERR_PTR.

Also, drop the unneeded NULL check before calling
ceph_osdc_put_request.

Fixes: 1cf7fdf52d5a ("ceph: convert readpage to fscache read helper")
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Suggested-by: Ilya Dryomov <idryomov@gmail.com>
Signed-off-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: Dan Carpenter <dan.carpenter@oracle.com>