staging: quickstart: fix up sysfs file permissions

Use the default DEVICE_ATTR_RO/RW macros to specify the file permissions
better, and make them easier to audit.

And did we really want any user to be able to write to this file, I kind
of doubt it...

Cc: Jiang Liu <jiang.liu@huawei.com>
Cc: Toshi Kani <toshi.kani@hp.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>