CHARGER_SBS should select REGMAP_I2C since it uses API(s) that are
provided by that Kconfig symbol.

Fixes these errors:

../drivers/power/supply/sbs-charger.c:149:21: error: variable ‘sbs_regmap’ has initializer but incomplete type
 static const struct regmap_config sbs_regmap = {
../drivers/power/supply/sbs-charger.c:150:3: error: ‘const struct regmap_config’ has no member named ‘reg_bits’
  .reg_bits = 8,
../drivers/power/supply/sbs-charger.c:155:23: error: ‘REGMAP_ENDIAN_LITTLE’ undeclared here (not in a function)
  .val_format_endian = REGMAP_ENDIAN_LITTLE, /* since based on SMBus */
../drivers/power/supply/sbs-charger.c: In function ‘sbs_probe’:
../drivers/power/supply/sbs-charger.c:183:17: error: implicit declaration of function ‘devm_regmap_init_i2c’; did you mean ‘devm_request_irq’? [-Werror=implicit-function-declaration]
  chip->regmap = devm_regmap_init_i2c(client, &sbs_regmap);
../drivers/power/supply/sbs-charger.c: At top level:
../drivers/power/supply/sbs-charger.c:149:35: error: storage size of ‘sbs_regmap’ isn’t known
 static const struct regmap_config sbs_regmap = {

Fixes: feb583e3 ("power: supply: add sbs-charger driver")
Reported-by: Martin Mokrejs <mmokrejs@fold.natur.cuni.cz>
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Tested-by: Martin Mokrejs <mmokrejs@fold.natur.cuni.cz>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>