rpmsg: Fix parameter naming for announce_create/destroy ops

The parameter associated to the announce_create and
announce_destroy ops functions is not an endpoint but a rpmsg device.

Signed-off-by: Arnaud Pouliquen <arnaud.pouliquen@foss.st.com>
Link: https://lore.kernel.org/r/20220425071723.774050-1-arnaud.pouliquen@foss.st.com
Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>