ath10k: Destroy QMI handle during driver unload

QMI handle was not destroyed during unload and server exit
and resulting in qmi handle leak.

Fix this problem by destroying the QMI handle during
driver unload and server exit.

Change-Id: I7557de7c2ff2cb7d82d6e8a3480e8d5f4be6a5f4
Signed-off-by: Govind Singh <govinds@codeaurora.org>