ARM: multi_v7_defconfig: update MFD_RK808 name

MFD_RK808 got split into an I2C and SPI part named MFD_RK8XX_I2C and
MFD_RK8XX_SPI. Since there are no known ARMv7 boards using the SPI
connected RK8XX chips (which are new), it is enough to just enable
the I2C option.

Reported-by: Marek Szyprowski <m.szyprowski@samsung.com>
Fixes: c20e8c5b ("mfd: rk808: Split into core and i2c")
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>