Staging: iio: Fix file header to match standards

Fix file header to match Linux Kernel style. Remove Free Software
Foundation reference to silence the checkpatch.pl warning.
Add driver description and correct spelling mistakes.

Signed-off-by: Cristina Opriceana <cristina.opriceana@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>