i2c: chips subdirectory is deprecated

Let driver authors know that drivers/i2c/chips is usually the wrong place
for new drivers.
Signed-off-by: Jean Delvare <khali@linux-fr.org>

drivers/i2c/chips/Makefile

 #
 # Makefile for miscellaneous I2C chip drivers.
 #
+# Think twice before you add a new driver to this directory.
+# Device drivers are better grouped according to the functionality they
+# implement rather than to the bus they are connected to. In particular:
+# * Hardware monitoring chip drivers go to drivers/hwmon
+# * RTC chip drivers go to drivers/rtc
+# * I/O expander drivers go to drivers/gpio
+#
 
 obj-$(CONFIG_DS1682)		+= ds1682.o
 obj-$(CONFIG_SENSORS_EEPROM)	+= eeprom.o