mwifiex: fix 'smatch' warning in preparing key_material cmd

The key length can be 32 bytes for TKIP and 16 bytes for AES_CMAC.
'smatch' warns on memcpy using key_len variable to copy data to
a 16 bytes buffer. Use fixed length to avoid the warning.
Reported-by: NDan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: NBing Zhao <bzhao@marvell.com>
Signed-off-by: NJohn W. Linville <linville@tuxdriver.com>

drivers/net/wireless/mwifiex/sta_cmd.c

@@ -690,7 +690,7 @@ mwifiex_cmd_802_11_key_material(struct mwifiex_private *priv,
 
 			memcpy(param->ipn, enc_key->pn, IGTK_PN_LEN);
 			memcpy(param->key, enc_key->key_material,
-			       enc_key->key_len);
+			       WLAN_KEY_LEN_AES_CMAC);
 
 			key_param_len = sizeof(struct mwifiex_cmac_param);
 			key_material->key_param_set.key_len =