Staging: IIO: Documentation: iio_utils: fix channel array generation.

The previous implementation flawed, in case some channels are not enabled.
The sorted array would then include channel information of disabled channels,
And misses the enabled ones, when the count is reached.
More troublesome, the loop would not even terminate.

The fix is twofold:

First we skip channels that are not enabled.
Then we use a tested bubble sort algorithm to sort the array.
Since we already allocated exactly the number of bytes we need.
We can exercise bubble sort on the original memory.
In all cases I've seen, the array is already sorted, so this sort
terminates immediately.

Changes since V1:
Fix coding style issues.

Signed-off-by: Michael Hennerich <michael.hennerich@analog.com>
Acked-by: Jonathan Cameron <jic23@cam.ac.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>