i2c: bcm2835: Set clock-stretch timeout to 35ms

The BCM2835 I2C blocks have a register to set the clock-stretch
timeout - how long the device is allowed to hold SCL low - in bus
cycles. The current driver doesn't write to the register, therefore
the default value of 64 cycles is being used for all devices.

Set the timeout to the value recommended for SMBus - 35ms.

See: https://github.com/raspberrypi/linux/issues/3064



Signed-off-by: Phil Elwell <phil@raspberrypi.org>