iio: light: fix improper return value

In function cm3232_reg_init(), it returns 0 even if the last call to
i2c_smbus_write_byte_data() returns a negative value (indicates error).
As a result, the return value may be inconsistent with the execution
status, and the caller of cm3232_reg_init() will not be able to detect
the error. This patch fixes the bug.

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=188641



Signed-off-by: Pan Bian <bianpan2016@163.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>