iio:light:ltr501: fix variable in ltr501_init

When filling data->als_contr, the register content read into status needs
to be used, instead of the return status value of regmap_read.

Fixes: 8592a7ee ("iio: ltr501: Add support for ltr559 chip")

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