s390/pci: set error state for unavailable functions

If we receive a notification that a pci function became unavailable we clean
up by removing the pci device. This can confuse the driver since the function
is already unaccessible. Improve this situation by setting an appropriate
error_state.

Reviewed-by: Gerald Schaefer <gerald.schaefer@de.ibm.com>
Signed-off-by: Sebastian Ott <sebott@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>