staging: rtl8723bs: replace _EXT_SUPPORTEDRATES_IE_

Replace unique _EXT_SUPPORTEDRATES_IE_ macro with kernel provided
WLAN_EID_EXT_SUPP_RATES from linux/ieee80211.h.

Signed-off-by: Ross Schmidt <ross.schm.dev@gmail.com>
Link: https://lore.kernel.org/r/20201208040733.379197-15-ross.schm.dev@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>