[SCSI] zfcp: Update dbf calls

Change the dbf data and functions to use the zfcp_dbf prefix
throughout the code. Also change the calls to dbf to use zfcp_dbf
instead of zfcp_adapter.

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@suse.de>