[SCSI] zfcp: Simplify get_adapter_by_busid

Call the helper function from cio instead looping through all zfcp
adapters.

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>