regulator: mcp16502: Select REGMAP_I2C to fix build error

Fix build error when CONFIG_REGMAP_I2C=m && CONFIG_REGULATOR_MCP16502=y.

drivers/regulator/mcp16502.o: In function `mcp16502_probe':
mcp16502.c:(.text+0xca): undefined reference to `__devm_regmap_init_i2c'

Signed-off-by: Axel Lin <axel.lin@ingics.com>
Signed-off-by: Mark Brown <broonie@kernel.org>