eeprom: at24: Improve confusing log message

Currently when binding to an spd EEPROM, the at24 drivers logs the
following message:

256 byte spd EEPROM, read-only, 0 bytes/write

The last part is confusing, as by definition you don't write to a
read-only EEPROM, plus "0 bytes/write" makes no sense whatsoever.

I propose to have a different message for read-only EEPROMs, which
does not include this last part.

Signed-off-by: Jean Delvare <jdelvare@suse.de>
Cc: Bartosz Golaszewski <bgolaszewski@baylibre.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Wolfram Sang <wsa@the-dreams.de>
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>