ceph: Deletion of unnecessary checks before two function calls

The functions ceph_put_snap_context() and iput() test whether their argument
is NULL and then return immediately. Thus the test around the call
is not needed.

This issue was detected by using the Coccinelle software.

Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
Signed-off-by: Ilya Dryomov <idryomov@redhat.com>