iio: light: veml6070: fix veml6070_read() return value

iio: light: veml6070: fix veml6070_read() return value

veml6070_read() computes the sensor value in ret but
returns 0 instead of the actual result. This causes
veml6070_read_raw() to always report 0.

Return the computed value instead of 0.

Running make W=1 returns no errors. I was unable
to test the patch because I do not have the hardware.
Found by code inspection.

Fixes: fc38525135dd ("iio: light: veml6070: use guard to handle mutex")
Signed-off-by: Aldo Conte <aldocontelk@gmail.com>
Reviewed-by: Nuno Sá <nuno.sa@analog.com>
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>