s390/pci: fix clp_get_state() handling of -ENODEV

With commit cc049eec ("s390/pci: simplify CLP List PCI handling")
clp_get_state() was changed to make use of the new clp_find_pci() helper
function to query a specific function. This however returns -ENODEV when
the device is not found at all and this error was passed to the caller.
It was missed however that the callers actually expect a success return
from clp_get_state() if the device is gone.

Fix this by handling the -ENODEV return of clp_find_pci() explicitly in
clp_get_state() returning success and setting the state parameter to
ZPCI_FN_STATE_RESERVED matching the design concept that a PCI function
that disappeared must have been resverved elsewhere. For all other error
returns continue to just pass them on to the caller.

Reviewed-by: Matthew Rosato <mjrosato@linux.ibm.com>
Fixes: cc049eec ("s390/pci: simplify CLP List PCI handling")
Signed-off-by: Niklas Schnelle <schnelle@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>