[SCSI] qla2xxx: Ensure the timer and DPC routines complete prior to midlayer tear-down.

Since the routines can/will use resources such as devices and
rports that aren't valid after midlayer tear-down, correct this
potential race, by stopping the offending during the early stages
of the remove() callback.

Signed-off-by: Andrew Vasquez <andrew.vasquez@qlogic.com>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>