staging: rtl8723bs: use WLAN_EID_RSN

Replace unique _WPA2_IE_ID_, EID_WPA2, and _RSN_IE_2_ with kernel provided
WLAN_EID_RSN from linux/ieee80211.h.

Signed-off-by: Ross Schmidt <ross.schm.dev@gmail.com>
Link: https://lore.kernel.org/r/20201208040733.379197-4-ross.schm.dev@gmail.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>