regulator: max77857: mark more functions static

regulator: max77857: mark more functions static

A few functions in the new driver are global but only used in this file:

drivers/regulator/max77857-regulator.c:209:5: error: no previous prototype for 'max77859_get_voltage_sel' [-Werror=missing-prototypes]
drivers/regulator/max77857-regulator.c:221:5: error: no previous prototype for 'max77859_set_current_limit' [-Werror=missing-prototypes]
drivers/regulator/max77857-regulator.c:235:5: error: no previous prototype for 'max77859_get_current_limit' [-Werror=missing-prototypes]

Mark them static, which produces potentially better code and avoids the warning.

Fixes: af71cccadeced ("regulator: max77857: Add ADI MAX77857/59/MAX77831 Regulator Support")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Link: https://lore.kernel.org/r/20230718193938.3593118-1-arnd@kernel.org
Signed-off-by: Mark Brown <broonie@kernel.org>