SG: Change sg_set_page() to take length and offset argument

Most drivers need to set length and offset as well, so may as well fold
those three lines into one.

Add sg_assign_page() for those two locations that only needed to set
the page, where the offset/length is set outside of the function context.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/drivers/s390/scsi/zfcp_erp.c b/drivers/s390/scsi/zfcp_erp.c
index 9438d0b..5552b75 100644
--- a/drivers/s390/scsi/zfcp_erp.c
+++ b/drivers/s390/scsi/zfcp_erp.c
@@ -322,9 +322,9 @@
 	if (address == NULL)
 		goto nomem;
 
-	zfcp_address_to_sg(address, send_els->req);
+	zfcp_address_to_sg(address, send_els->req, sizeof(struct zfcp_ls_adisc));
 	address += PAGE_SIZE >> 1;
-	zfcp_address_to_sg(address, send_els->resp);
+	zfcp_address_to_sg(address, send_els->resp, sizeof(struct zfcp_ls_adisc_acc));
 	send_els->req_count = send_els->resp_count = 1;
 
 	send_els->adapter = adapter;
@@ -336,9 +336,6 @@
 	adisc = zfcp_sg_to_address(send_els->req);
 	send_els->ls_code = adisc->code = ZFCP_LS_ADISC;
 
-	send_els->req->length = sizeof(struct zfcp_ls_adisc);
-	send_els->resp->length = sizeof(struct zfcp_ls_adisc_acc);
-
 	/* acc. to FC-FS, hard_nport_id in ADISC should not be set for ports
 	   without FC-AL-2 capability, so we don't set it */
 	adisc->wwpn = fc_host_port_name(adapter->scsi_host);