regulator: qcom_spmi: Constify struct regulator_ops

regulator: qcom_spmi: Constify struct regulator_ops

These are never modified, so make them const to allow the compiler to
put them in read-only memory.

Before:
   text    data     bss     dec     hex filename
  20362    2592     152   23106    5a42 drivers/regulator/qcom_spmi-regulator.o

After:
   text    data     bss     dec     hex filename
  21814    1140     152   23106    5a42 drivers/regulator/qcom_spmi-regulator.o

Signed-off-by: Rikard Falkeborn <rikard.falkeborn@gmail.com>
Link: https://lore.kernel.org/r/20200629194632.8147-3-rikard.falkeborn@gmail.com
Signed-off-by: Mark Brown <broonie@kernel.org>