staging: wfx: Use flex_array_size() helper in memcpy()

Make use of the flex_array_size() helper to calculate the size of a
flexible array member within an enclosing structure.

This helper offers defense-in-depth against potential integer
overflows, while at the same time makes it explicitly clear that
we are dealing with a flexible array member.

Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Link: https://lore.kernel.org/r/20200729233557.GA17693@embeddedor
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/wfx/hif_tx_mib.c

@@ -113,7 +113,7 @@ int hif_set_beacon_filter_table(struct wfx_vif *wvif, int tbl_len,
 	if (!val)
 		return -ENOMEM;
 	val->num_of_info_elmts = cpu_to_le32(tbl_len);
-	memcpy(val->ie_table, tbl, tbl_len * sizeof(*tbl));
+	memcpy(val->ie_table, tbl, flex_array_size(val, ie_table, tbl_len));
 	ret = hif_write_mib(wvif->wdev, wvif->id,
 			    HIF_MIB_ID_BEACON_FILTER_TABLE, val, buf_len);
 	kfree(val);