wifi: ath10k: Avoid vdev delete timeout when firmware is already down

wifi: ath10k: Avoid vdev delete timeout when firmware is already down

In some scenarios, the firmware may be stopped before the interface is
removed, either due to a crash or because the remoteproc (e.g., MPSS)
is shut down early during system reboot or shutdown.

This leads to a delay during interface teardown, as the driver waits for
a vdev delete response that never arrives, eventually timing out.

Example (SNOC):
$ echo stop > /sys/class/remoteproc/remoteproc0/state
[ 71.64] remoteproc remoteproc0: stopped remote processor modem
$ reboot
[ 74.84] ath10k_snoc c800000.wifi: failed to transmit packet, dropping: -108
[ 74.84] ath10k_snoc c800000.wifi: failed to submit frame: -108
[...]
[ 82.39] ath10k_snoc c800000.wifi: Timeout in receiving vdev delete response

To avoid this, skip waiting for the vdev delete response if the firmware is
already marked as unreachable (`ATH10K_FLAG_CRASH_FLUSH`), similar to how
`ath10k_mac_wait_tx_complete()` and `ath10k_vdev_setup_sync()` handle this case.

Signed-off-by: Loic Poulain <loic.poulain@oss.qualcomm.com>
Link: https://patch.msgid.link/20250522131704.612206-1-loic.poulain@oss.qualcomm.com
Signed-off-by: Jeff Johnson <jeff.johnson@oss.qualcomm.com>