wifi: ath12k: fix crash when unbinding

wifi: ath12k: fix crash when unbinding

If there is an error during some initialization related to firmware,
the function ath12k_dp_cc_cleanup is called to release resources.
However this is released again when the device is unbinded (ath12k_pci),
and we get:
BUG: kernel NULL pointer dereference, address: 0000000000000020
at RIP: 0010:ath12k_dp_cc_cleanup.part.0+0xb6/0x500 [ath12k]
Call Trace:
ath12k_dp_cc_cleanup
ath12k_dp_free
ath12k_core_deinit
ath12k_pci_remove
...

The issue is always reproducible from a VM because the MSI addressing
initialization is failing.

In order to fix the issue, just set to NULL the released structure in
ath12k_dp_cc_cleanup at the end.

cc: stable@vger.kernel.org
Fixes: d889913205cf ("wifi: ath12k: driver for Qualcomm Wi-Fi 7 devices")
Signed-off-by: Jose Ignacio Tornos Martinez <jtornosm@redhat.com>
Link: https://patch.msgid.link/20241017181004.199589-2-jtornosm@redhat.com
Signed-off-by: Jeff Johnson <quic_jjohnson@quicinc.com>