staging: rtl8192u: move debug files to debugfs

staging: rtl8192u: move debug files to debugfs

There are 4 debug files created under /proc/net/[Devname].
Due to this is purely for debuging as files are created read only,
move this to debugfs like other NIC drivers do instead of using procfs.
The directory structure will be like the following

  /sys/kernel/debug/r8192u_usb/wlan0/stats-rx
  /sys/kernel/debug/r8192u_usb/wlan0/stats-rx
  /sys/kernel/debug/r8192u_usb/wlan0/stats-ap
  /sys/kernel/debug/r8192u_usb/wlan0/registers

This is also to prepare for address rmmod warn issue.

Reviewed-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Tong Zhang <ztong0001@gmail.com>
Link: https://lore.kernel.org/r/20220730033335.74153-4-ztong0001@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>