ARM: dts: bcm2835: fix i2c0 pins

According to the BCM2835 ARM Peripherals document i2c0 doesn't map to pins 32,
34 but to 28, 29.

Fixes: 21ff8439 ("ARM: dts: bcm283x: Define standard pinctrl groups in the gpio node.")
Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Reviewed-by: Eric Anholt <eric@anholt.net>