regulator: lp8788: constify regulator_ops structures

The regulator_ops structures are never modified, so declare them as const.

Done with the help of Coccinelle.

Signed-off-by: Julia Lawall <Julia.Lawall@lip6.fr>
Acked-by: Milo Kim <milo.kim@ti.com>
Signed-off-by: Mark Brown <broonie@kernel.org>