[SCSI] zfcp: wait on SCSI work to be finished before proceeding with init dev

Due to the character of a scheduled work we cannot guarantee the
LUN register to be finished before an initial device tries to use it.
Therefor we have to wait for PENDING_SCSI_WORK flag to be cleared
before proceeding.

Signed-off-by: Swen Schillig <swen@vnet.ibm.com>
Signed-off-by: Christof Schmitt <christof.schmitt@de.ibm.com>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>