eeprom: at25: Remove in kernel API for accessing the EEPROM

The setup() callback is not used by any in kernel code. Remove it.
Any new code which requires access to the eeprom can use the NVMEM
API.

Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Acked-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Acked-by: Wolfram Sang <wsa@the-dreams.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>