ixgbevf: Check for adapter removal on register writes

Prevent writes to an adapter that has been detected as removed
by a previous failing read.

Signed-off-by: Mark Rustad <mark.d.rustad@intel.com>
Tested-by: Phil Schmitt <phillip.j.schmitt@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>