staging: wfx: remove useless header inclusions

In order to keep the compilation times reasonable, we try to only
include the necessary headers (especially header included from other
headers).

This patch clean up unnecessary headers inclusions.

Signed-off-by: Jérôme Pouiller <jerome.pouiller@silabs.com>
Link: https://lore.kernel.org/r/20200505123757.39506-13-Jerome.Pouiller@silabs.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>