staging: dgnc: Fix included header from 'asm'

This commit fixes the checkpatch warning:

drivers/staging/dgnc/dgnc_neo.c:37:
    WARNING: Use #include <linux/io.h> instead of <asm/io.h>

Signed-off-by: Konrad Zapalowicz <bergo.torino@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>