mwifiex: fix Coverity SCAN CID 709078: Resource leak (RESOURCE_LEAK)

> *. CID 709078: Resource leak (RESOURCE_LEAK)
> 	- drivers/net/wireless/mwifiex/cfg80211.c, line: 935
> Assigning: "bss_cfg" = storage returned from "kzalloc(132UL, 208U)"
> 	- but was not free
> drivers/net/wireless/mwifiex/cfg80211.c:935

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