eeprom: at24: fix I2C device selection for runtime PM

The at24 driver creates dummy I2C devices to access offsets in the chip
that are outside the area supported using a single I2C address. It is not
meaningful to use runtime PM to such devices; the system firmware (ACPI)
does not know about these devices nor runtime PM was enabled for them.
Always use the real device instead of the dummy ones.

Fixes: 98e82010 ("eeprom: at24: enable runtime pm support")
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Tested-by: Sven Van Asbroeck on a 24AA16/24LC16B <svendev@arcx.com>
[Bartosz: rebased on top of previous fixes for 4.15, tweaked the
          commit message]
[Sven: fixed Bartosz's rebase]
Signed-off-by: Sven Van Asbroeck <svendev@arcx.com>
Signed-off-by: Bartosz Golaszewski <brgl@bgdev.pl>