regulator: tps65090: Fix tps65090 typos in example

Specification and existing device trees use vsys-l{1,2}-supply,
not vsys_l{1,2}-supply. Fix the example to match the specification.

Fixes: 21d2202158e9 ("mfd: tps65090: add DT support for tps65090")
Reviewed-by: Doug Anderson <dianders@chromium.org>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Andreas Färber <afaerber@suse.de>
Reviewed-by: Javier Martinez Canillas <javier.martinez@collabora.co.uk>
Signed-off-by: Mark Brown <broonie@linaro.org>