Fix sparse warning:
drivers/regulator/max77857-regulator.c:430:28: warning: symbol 'max77857_id' was not declared. Should it be static?

max77857_id is not used outside the source file. Make it static.
Signed-off-by: Yue Haibing <yuehaibing@huawei.com>
Link: https://patch.msgid.link/20240801114536.472796-1-yuehaibing@huawei.comSigned-off-by: Mark Brown <broonie@kernel.org>