staging: wfx: fix spelling mistake "hexdecimal" -> "hexadecimal"

There is a spelling mistake in the documentation and a module parameter
description. Fix these.

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Link: https://lore.kernel.org/r/20191008082205.19740-1-colin.king@canonical.com


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