mwifiex: remove unnecessary free_priv handler

Cfg80211 stack allocates private area for driver use in
struct cfg80211_bss. It will be freed by stack in bss_release().
Driver don't need to worry about it.

In mwifiex driver, we use the private area just to store band
information(u8). We don't allocate memory explicitly and store
it's pointer in bss->priv. Hence we don't have any cleanup work
to do in free_priv handler. Currently we try to free the allocated
private area in free_priv handler which is not correct.

This patch removes unnecessary free_priv handler.

Signed-off-by: Amitkumar Karwar <akarwar@marvell.com>
Signed-off-by: Bing Zhao <bzhao@marvell.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>