CHROMIUM: mwifiex: return -EBUSY if specific scan request cannot be honored

CHROMIUM: mwifiex: return -EBUSY if specific scan request cannot be honored

Previous patch "mwifiex: return -EBUSY if scan request cannot.."
corrected regular scan request only. There is another case for
specific scan that needs the same handling.

BUG=chrome-os-partner:15087
TEST=(1) On Wi-Fi Network Settings, enable Wi-Fi and connect to AP,
then disable Wi-Fi. Repeat above test multiple time.
(2) Associated to AP and run "iw mlan0 scan" in a 'while' loop.

Change-Id: I8168eb109983223b7f27af6f8d84048fbd276811
Signed-off-by: Bing Zhao <bzhao@marvell.com>
Signed-off-by: Paul Stewart <pstew@chromium.org>
Reviewed-on: https://gerrit.chromium.org/gerrit/35478
Reviewed-by: Ryan Cairns <rtc@chromium.org>