mwifiex: overwrite earlier IE buffers for new set IE request

All IE buffers are freshly supplied. In such case, there is no need
to preserve earlier buffers with same management mask and index.

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