eeprom: at24: use a helper variable for dev

We use the &client->dev construct all over in at24_probe(). Use
a helper variable which is more readable and allows to avoid a couple
unnecessary line breaks.

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>