mwifiex: reset scan_processing flag in failure cases

mwifiex: reset scan_processing flag in failure cases

scan_processing flag should be reset when scan request is failed
due to some reasons Ex. memory allocation failure etc. Otherwise
further scan requests will be blocked.

Signed-off-by: Amitkumar Karwar <akarwar@marvell.com>
Signed-off-by: Bing Zhao <bzhao@marvell.com>
BUG=chrome-os-partner:14486
TEST=AP doing WPA and group rekeying every 600s;
DUT connects and is doing a ping with 2 second interval;
On DUT, run "while true; do iw mlan0 scan > /dev/null; done"

Change-Id: Ie0dcf5ac74cdec5c9ae3261180923a1405d5e2c7
Reviewed-on: https://gerrit.chromium.org/gerrit/34715
Reviewed-by: Paul Stewart <pstew@chromium.org>
Commit-Ready: Bing Zhao <bzhao@marvell.com>
Tested-by: Bing Zhao <bzhao@marvell.com>