staging: iio: add proper SPDX identifiers to remaining driver files

There are a number of IIO staging drivers that do not have a proper SPDX
identifier on it. So fix that up and at the same time, remove the "free
form" license text, as that's pretty much impossible for any tool to
parse.

Cc: Lars-Peter Clausen <lars@metafoo.de>
Cc: Michael Hennerich <Michael.Hennerich@analog.com>
Cc: Jonathan Cameron <jic23@kernel.org>
Cc: Hartmut Knaack <knaack.h@gmx.de>
Cc: Peter Meerwald-Stadler <pmeerw@pmeerw.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

iio: ad9834 convert symbolic permissions to octal

Remove checkpatch warnings by converting symbolic S_IRUGO and S_IWUSR
permissions to octal

Signed-off-by: Quentin Swain <dudebrobro179@gmail.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

Staging: iio: Added define guards where needed

The following files were added define guards to prevent multiple
inclusion.

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

staging: iio: frequency: remove unnecessary semicolon

This fixes the checkpatch.pl warning:
WARNING: macros should not use a trailing semicolon

Signed-off-by: Roxana Blaj <roxanagabriela10@gmail.com>
Acked-by: Daniel Baluta <daniel.baluta@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

iio: frequency: Update DDS drivers to use new channel naming convention

Signed-off-by: Michael Hennerich <michael.hennerich@analog.com>
Acked-by: Jonathan Cameron <jic23@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

iio: Rename iio/dds to iio/frequency

Generalize naming to allow other frequency synthesis techniques as well.
No functional changes.

Signed-off-by: Michael Hennerich <michael.hennerich@analog.com>
Acked-by: Jonathan Cameron <jic23@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>