staging: r8188eu: get reason code from mgmt struct

Read the deauth reson code from the newly added mgmt structure instead of
calculating the offset ourselves.
Signed-off-by: Martin Kaiser <martin@kaiser.cx>
Tested-by: Philipp Hortmann <philipp.g.hortmann@gmail.com> # Edimax N150
Acked-by: Pavel Skripkin <paskripkin@gmail.com>
Link: https://lore.kernel.org/r/20221015152440.232281-3-martin@kaiser.cxSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/r8188eu/core/rtw_mlme_ext.c

@@ -1473,7 +1473,7 @@ unsigned int OnDeAuth(struct adapter *padapter, struct recv_frame *precv_frame)
 		_set_timer(&pwdinfo->reset_ch_sitesurvey, 10);
 	}
 
-	reason = le16_to_cpu(*(__le16 *)(pframe + WLAN_HDR_A3_LEN));
+	reason = le16_to_cpu(mgmt->u.disassoc.reason_code);
 
 	if (check_fwstate(pmlmepriv, WIFI_AP_STATE)) {
 		struct sta_info *psta;