staging: tidspbridge: remove redundant NULL check before delete_msg_mgr().

delete_msg_mgr on a NULL pointer is a no-op, so the NULL check in
bridge_msg_delete can be removed.

Signed-off-by: Cyril Roelandt <tipecaml@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>