staging: dgnc: dgnc_sysfs *_ATTR() macros convert

Convert DRIVER_ATTR() macro with DRIVER_ATTR_RO/RW and
DEVICE_ATTR() macro with DEVICE_ATTR_RO()

Signed-off-by: Matias Mucciolo <mmucciolo@suteba.org.ar>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>