scsi: mpt3sas: Cancel the running work during host reset

It is not recommended to issue back-to-back host reset without any delay.
However, if someone issues back-to-back host reset then we observe that
target devices get unregistered and re-register with SML.  And if OS drive
is behind the HBA when it gets unregistered, then file-system goes into
read-only mode.

Normally during host reset, driver marks accessible target devices as
responding and triggers the event MPT3SAS_REMOVE_UNRESPONDING_DEVICES to
remove any non-responding devices through FW worker thread. While
processing this event, driver unregisters the non-responding devices and
clears the responding flag for all the devices.

Currently, during host reset, driver is cancelling only those Firmware
event works which are pending in Firmware event workqueue. It is not
cancelling work which is currently running. Change the driver to cancel all
events.

Link: https://lore.kernel.org/r/1596096229-3341-4-git-send-email-suganath-prabu.subramani@broadcom.com
Signed-off-by: Suganath Prabu S <suganath-prabu.subramani@broadcom.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>