igbvf: convert msleep to mdelay in atomic context

This fixes a "scheduling while atomic" splat seen with
CONFIG_DEBUG_ATOMIC_SLEEP enabled.

Signed-off-by: Greg Edwards <gedwards@ddn.com>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>