staging: rtl8723au: core: avoid bitwise arithmetic with forced endianness

This fixes bitwise arithmetic performed on the host on a variable
previously converted to little-endian, and subsequently converted
again to little-endian:
  - issue_action_BA23a() called with "status" crafted in host byte order
  - "status" converted to LE
  - bitwise arithmetic on the (LE) "status", performed with masks and
    shifts in host byte order
  - result converted to LE (again) and stored in device structure

Sparse warning addressed by this patch:
  drivers/staging/rtl8723au/core/rtw_mlme_ext.c:3806:16: warning: incorrect type in assignment (different base types)
  drivers/staging/rtl8723au/core/rtw_mlme_ext.c:3806:16:    expected unsigned short [unsigned] status
  drivers/staging/rtl8723au/core/rtw_mlme_ext.c:3806:16:    got restricted __le16 [usertype] <noident>

Additional notes: initial cpu_to_le16 was introduced by kernel bulk
  commit 5e93f352 "staging: r8723au: Add source files for new driver
  - part 1", initially from github according to commit description. On
  github, this traces back to another bulk commit: 2896bda04353 "Add
  new files in core directory", which is the 1st version of the
  driver.
Signed-off-by: David Decotigny <ddecotig@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/rtl8723au/core/rtw_mlme_ext.c

@@ -3803,8 +3803,6 @@ void issue_action_BA23a(struct rtw_adapter *padapter,
 
 	pattrib->pktlen = sizeof(struct ieee80211_hdr_3addr) + 1;
 
-	status = cpu_to_le16(status);
-
 	switch (action) {
 	case WLAN_ACTION_ADDBA_REQ:
 		pattrib->pktlen += sizeof(mgmt->u.action.u.addba_req);