rtc: rv3029: hide unused i2c device table

The added support for SPI mode made it possible to configure the driver
when I2C is disabled, leaving an unused device table:

drivers/rtc/rtc-rv3029c2.c:794:29: error: 'rv3029_id' defined but not used [-Werror=unused-variable]

This moves the table inside of the #ifdef section that has the
only user, to avoid the harmless warning.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Fixes: d08f50dd0afc ("rtc: rv3029: Add support of RV3049")
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>