mwifiex: complete last internal scan

We are waiting on first scan command of internal scan request
before association, so we should complete on last internal scan
command response.

Cc: <stable@vger.kernel.org> # 3.8
Tested-by: Daniel Drake <dsd@laptop.org>
Tested-by: Marco Cesarano <marco@marvell.com>
Signed-off-by: Bing Zhao <bzhao@marvell.com>
Signed-off-by: Amitkumar Karwar <akarwar@marvell.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>