iio:light:cm3323: pass up error value

cm3323_get_it_bits() returns a valid error code, so pass it up in
cm3323_read_raw().

Signed-off-by: Hartmut Knaack <knaack.h@gmx.de>
Reviewed-by: Daniel Baluta <daniel.baluta@intel.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>