regulator: ltc3676: Constify ltc3676_regulators

regulator: ltc3676: Constify ltc3676_regulators

ltc3676_regulators is not modified and can be made const to allow the
compiler to put it in read-only memory.

Before:
   text    data     bss     dec     hex filename
   4361    2064       8    6433    1921 drivers/regulator/ltc3676.o

After:
   text    data     bss     dec     hex filename
   6121     304       8    6433    1921 drivers/regulator/ltc3676.o

Signed-off-by: Rikard Falkeborn <rikard.falkeborn@gmail.com>
Link: https://lore.kernel.org/r/20200617223247.25566-4-rikard.falkeborn@gmail.com
Signed-off-by: Mark Brown <broonie@kernel.org>