iio: chemical: SENSEAIR_SUNRISE_CO2 depends on I2C

Fix kconfig symbol dependency warning:

WARNING: unmet direct dependencies detected for REGMAP_I2C
  Depends on [n]: I2C [=n]
  Selected by [y]:
  - SENSEAIR_SUNRISE_CO2 [=y] && IIO [=y]

Fixes: c397894e24 ("iio: chemical: Add Senseair Sunrise 006-0-007 drive")
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Jacopo Mondi <jacopo@jmondi.org>
Cc: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Cc: linux-iio@vger.kernel.org
Link: https://lore.kernel.org/r/20211002232803.5108-1-rdunlap@infradead.org
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/chemical/Kconfig

@@ -172,6 +172,7 @@ config SPS30_SERIAL
 
 config SENSEAIR_SUNRISE_CO2
 	tristate "Senseair Sunrise 006-0-0007 CO2 sensor"
+	depends on I2C
 	select REGMAP_I2C
 	help
 	  Say yes here to build support for Senseair Sunrise 006-0-0007 CO2