regulator: lp87565: Fix missing register for LP87565_BUCK_0

LP87565_BUCK_0 is missed, fix it.

Fixes: f0168a9b ("regulator: lp87565: Add support for lp87565 PMIC regulators")
Signed-off-by: Axel Lin <axel.lin@ingics.com>
Reviewed-by: Keerthy <j-keerthy@ti.com>
Signed-off-by: Mark Brown <broonie@kernel.org>