mwifiex: fix memory leak issue for ibss join

For IBSS join if the requested SSID matches current SSID,
it returns without freeing the allocated beacon IE buffer.

Cc: <stable@vger.kernel.org> # 3.10+
Signed-off-by: Ujjal Roy <royujjal@gmail.com>
Signed-off-by: Bing Zhao <bzhao@marvell.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>