iio: core: check 'info' value before registering the device

When the 'info' structure inside indio_dev is left uninitialized,
a segmentation fault occurs.

Check the 'info' value before using it and if it is equal to
NULL, return with -EINVAL.

Signed-off-by: Andi Shyti <andi@etezian.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>