eeprom: at24: remove nvmem_config from at24_data

This structure only needs to exist during the call to nvmem_register().

Signed-off-by: Bartosz Golaszewski <brgl@bgdev.pl>
Tested-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>