Without I2C, we get a link failure:

drivers/ptp/ptp_clockmatrix.o: In function `idtcm_xfer.isra.3':
ptp_clockmatrix.c:(.text+0xcc): undefined reference to `i2c_transfer'
drivers/ptp/ptp_clockmatrix.o: In function `idtcm_driver_init':
ptp_clockmatrix.c:(.init.text+0x14): undefined reference to `i2c_register_driver'
drivers/ptp/ptp_clockmatrix.o: In function `idtcm_driver_exit':
ptp_clockmatrix.c:(.exit.text+0x10): undefined reference to `i2c_del_driver'

Fixes: 3a6ba7dc ("ptp: Add a ptp clock driver for IDT ClockMatrix.")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Vincent Cheng <vincent.cheng.xh@renesas.com>
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>