libertas: use mesh_wdev->ssid instead of priv->mesh_ssid

With the commit e86dc1ca46 ("Libertas: cfg80211 support") we've lost
the ability to actually set the Mesh SSID from userspace.
NL80211_CMD_SET_INTERFACE with NL80211_ATTR_MESH_ID sets the mesh point
interface's ssid field. Let's use that one for the Libertas Mesh
operation

Signed-off-by: Lubomir Rintel <lkundrak@v3.sk>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>

drivers/net/wireless/marvell/libertas/dev.h

@@ -58,8 +58,6 @@ struct lbs_private {
 #ifdef CONFIG_LIBERTAS_MESH
 	struct lbs_mesh_stats mstats;
 	uint16_t mesh_tlv;
-	u8 mesh_ssid[IEEE80211_MAX_SSID_LEN + 1];
-	u8 mesh_ssid_len;
 	u8 mesh_channel;
 #endif