The qmi infrastructure sends the client a del_server
event when the client releases its qmi handle. This
is not the msg indicating the actual qmi server exiting.
In such cases the del_server msg should not be processed,
since the wifi firmware does not reset its qmi state.

Hence skip the processing of del_server event when the
driver is unloading.

Tested HW: WCN3990
Tested FW: WLAN.HL.3.1-01040-QCAHLSWMTPLZ-1

Fixes: ba94c753 ("ath10k: add QMI message handshake for wcn3990 client")
Signed-off-by: Rakesh Pillai <pillair@codeaurora.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/1588663061-12138-1-git-send-email-pillair@codeaurora.org