mwifiex: scan delay timer cleanup in unload path

mwifiex: scan delay timer cleanup in unload path

Return from scan delay timer routine if surprise_removed flag
is true. Also, cancel the timer in unload path.

This fixes a crash when scan delay timer accesses structures
that have been freed already.

Tested with "iwlist mlan0 scan & sleep 1; rmmod mwifiex_sdio"

BUG=None
TEST="iwlist mlan0 scan & sleep 1; rmmod mwifiex_sdio";
"echo scan > /sys/kernel/debug/kmemleak; cat /sys/kernel/debug/kmemleak"

Change-Id: Ia69b70ecc8b208fce4c2c3f39ec6e2d4042962f6
Reported-by: Daniel Drake <dsd@laptop.org> [OLPC]
Tested-by: Daniel Drake <dsd@laptop.org> [OLPC]
Signed-off-by: Amitkumar Karwar <akarwar@marvell.com>
Signed-off-by: Bing Zhao <bzhao@marvell.com>
Reviewed-on: https://gerrit.chromium.org/gerrit/50685
Reviewed-by: Paul Stewart <pstew@chromium.org>