ionic: prevent pci disable of already disabled device

If a reset fails, the PCI device is left in a disabled
state, so don't try to disable it again on driver remove.
This prevents a scary looking WARN trace in the kernel log.

    ionic 0000:2b:00.0: disabling already-disabled device

Signed-off-by: Shannon Nelson <shannon.nelson@amd.com>
Reviewed-by: Brett Creeley <brett.creeley@amd.com>
Signed-off-by: David S. Miller <davem@davemloft.net>