regulator: stw481x-vmmc: Constify static structs

regulator: stw481x-vmmc: Constify static structs

The only usage of stw481x_vmmc_ops is to assign its address to the ops
field in the regulator_desc struct which is a const pointer.

The only usage of vmmc_regulator is to pass its address to
of_get_regulator_init_data() and devm_regulator_register(), both which
take const pointers.

Make both of them const to allow the compiler to put them in read-only
memory.

Signed-off-by: Rikard Falkeborn <rikard.falkeborn@gmail.com>
Link: https://lore.kernel.org/r/20200913084114.8851-4-rikard.falkeborn@gmail.com
Signed-off-by: Mark Brown <broonie@kernel.org>