staging: rtl8723bs: core: Replace sprintf with scnprintf

staging: rtl8723bs: core: Replace sprintf with scnprintf

The use of sprintf with format string here means that there is a risk
that the writes will go out of bounds, replace it with scnprintf.

In on_action_public_default the variable "cnt" isn't being used for
anything meaningful so remove it.

Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Candy Febriyanto <cfebriyanto@gmail.com>
Link: https://lore.kernel.org/r/6c260641164d6856fc4447555fe739124cb27c19.1614610197.git.cfebriyanto@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>