s390/pci: fix three typos in comments

Found and fixed these while working on synchronizing the state
handling of zpci_dev's.

Signed-off-by: Gerd Bayer <gbayer@linux.ibm.com>
Reviewed-by: Niklas Schnelle <schnelle@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>