Add a workaround for lost MSI interrupts.  There is a race condition in
the HW in which future interrupts could be missed.  The workaround is to
toggle the MSI irq mask.

Added cleanup based on comments from Andrew Morton.
Signed-off-by: NAyaz Abdulla <aabdulla@nvidia.com>
Cc: Manfred Spraul <manfred@colorfullife.com>
Cc: Jeff Garzik <jeff@garzik.org>
Cc: <stable@kernel.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NJeff Garzik <jgarzik@redhat.com>