eeprom: at24: check at24_read/write arguments

So far we completely rely on the caller to provide valid arguments.
To be on the safe side perform an own sanity check.

Cc: stable@vger.kernel.org
Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: Bartosz Golaszewski <brgl@bgdev.pl>