greybus: es2: fix driver name collision with es1

Both ES1 and ES2 drivers cannot be loaded due to a driver name conflict.
Give ES2 driver the correct name.

Signed-off-by: Rob Herring <rob.herring@linaro.org>
Reviewed-by: Alex Elder <elder@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>