i2c: cbus-gpio: set atomic transfer callback

CBUS transfers have always been atomic, but after commit 63b96983
("i2c: core: introduce callbacks for atomic transfers") we started to see
warnings during e.g. poweroff as the atomic callback is not explicitly set.
Fix that.

Fixes the following WARNING seen during Nokia N810 power down:

[  786.570617] reboot: Power down
[  786.573913] ------------[ cut here ]------------
[  786.578826] WARNING: CPU: 0 PID: 672 at drivers/i2c/i2c-core.h:40 i2c_smbus_xfer+0x100/0x110
[  786.587799] No atomic I2C transfer handler for 'i2c-2'

Fixes: 63b96983 ("i2c: core: introduce callbacks for atomic transfers")
Signed-off-by: Aaro Koskinen <aaro.koskinen@iki.fi>
Signed-off-by: Wolfram Sang <wsa@kernel.org>

drivers/i2c/busses/i2c-cbus-gpio.c

@@ -195,8 +195,9 @@ static u32 cbus_i2c_func(struct i2c_adapter *adapter)
 }
 
 static const struct i2c_algorithm cbus_i2c_algo = {
-	.smbus_xfer	= cbus_i2c_smbus_xfer,
-	.functionality	= cbus_i2c_func,
+	.smbus_xfer		= cbus_i2c_smbus_xfer,
+	.smbus_xfer_atomic	= cbus_i2c_smbus_xfer,
+	.functionality		= cbus_i2c_func,
 };
 
 static int cbus_i2c_remove(struct platform_device *pdev)