iio: tcs3472: power down chip on probe failure

iio: tcs3472: power down chip on probe failure

If tcs3472_probe() fails after enabling the chip (by writing PON | AEN
to the ENABLE register), the error paths return without powering down
the device.

Add an 'error_powerdown' label at the end of the cleanup chain that
calls tcs3472_powerdown() to power down the chip. The existing label
cascade is rerouted to fall through to the new label.

Move tcs3472_powerdown() above tcs3472_probe() so the probe can call
it without a forward declaration.

Found by code inspection while reviewing the probe error paths in
preparation for the devm_ conversion.

Fixes: eb869ade30a6 ("iio: Add tcs3472 color light sensor driver")
Signed-off-by: Aldo Conte <aldocontelk@gmail.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>