ntb_transport: Check the number of spads the hardware supports

I'm working on hardware that currently has a limited number of
scratchpad registers and ntb_ndev fails with no clue as to why. I
feel it is better to fail early and provide a reasonable error message
then to fail later on.

The same is done to ntb_perf, but it doesn't currently require enough
spads to actually fail. I've also removed the unused SPAD_MSG and
SPAD_ACK enums so that MAX_SPAD accurately reflects the number of
spads used.

Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
Acked-by: Dave Jiang <dave.jiang@intel.com>
Signed-off-by: Jon Mason <jdmason@kudzu.us>
diff --git a/drivers/ntb/test/ntb_perf.c b/drivers/ntb/test/ntb_perf.c
index 30635c8..4368519 100644
--- a/drivers/ntb/test/ntb_perf.c
+++ b/drivers/ntb/test/ntb_perf.c
@@ -143,8 +143,6 @@
 	VERSION = 0,
 	MW_SZ_HIGH,
 	MW_SZ_LOW,
-	SPAD_MSG,
-	SPAD_ACK,
 	MAX_SPAD
 };
 
@@ -696,6 +694,12 @@
 	int node;
 	int rc = 0;
 
+	if (ntb_spad_count(ntb) < MAX_SPAD) {
+		dev_err(&ntb->dev, "Not enough scratch pad registers for %s",
+			DRIVER_NAME);
+		return -EIO;
+	}
+
 	node = dev_to_node(&pdev->dev);
 
 	perf = kzalloc_node(sizeof(*perf), GFP_KERNEL, node);