qaic: fix a possible race with dbc release

Consider following situation:

Activate network n1 using CPU c1 on host, and this activation allocates
a dbc_id. We populate software structure for that dbc_id.
During deactivation, firmware first frees that dbc and then kernel
driver nukes associated resources.
Before, kernel could have nuked associated resources, another network n2
is activated using another CPU c2, and firmware allocates same dbc_id
for this network. This would raise a race condition.

Fix this race.

Change-Id: I27f07c147d2db31dd9787af0540c67c4b791ae76
Signed-off-by: Pratyush Anand <pratanan@codeaurora.org>