eeprom: at24: Remove set but not used variable 'addr'

Fixes gcc '-Wunused-but-set-variable' warning:

drivers/misc/eeprom/at24.c: In function at24_make_dummy_client:
drivers/misc/eeprom/at24.c:514:21: warning: variable addr set but not used [-Wunused-but-set-variable]

It's not used since commit e7308628 ("eeprom:
at24: use devm_i2c_new_dummy_device()")

Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>