cxl/test: Replace ENXIO with EBUSY for inject poison limit reached

The CXL driver was recently updated to return EBUSY rather than
ENXIO when the device reports that an injection request exceeds
the device's limit. That change to EBUSY allows debug users to
differentiate between limit reached and inject failures for any
other reason.

Change cxl-test to also return EBUSY and tidy up the dev_dbg()
messaging to emit the correct limit.

Reminder: the cxl-test per device injection limit is a configurable
attribute: /sys/bus/platform/drivers/cxl_mock_mem/poison_inject_max

Signed-off-by: Alison Schofield <alison.schofield@intel.com>
Tested-by: Xingtao Yao <yaoxt.fnst@fujitsu.com>
Reviewed-by: Dan Williams <dan.j.williams@intel.com>
Reviewed-by: Davidlohr Bueso <dave@stgolabs.net>
Link: https://patch.msgid.link/ba1b80e1658b644d85d0d5e2287112d00a48b9cf.1720316188.git.alison.schofield@intel.com
Signed-off-by: Dave Jiang <dave.jiang@intel.com>

tools/testing/cxl/test/mem.c

@@ -1135,27 +1135,28 @@ static bool mock_poison_dev_max_injected(struct cxl_dev_state *cxlds)
 	return (count >= poison_inject_dev_max);
 }
 
-static bool mock_poison_add(struct cxl_dev_state *cxlds, u64 dpa)
+static int mock_poison_add(struct cxl_dev_state *cxlds, u64 dpa)
 {
+	/* Return EBUSY to match the CXL driver handling */
 	if (mock_poison_dev_max_injected(cxlds)) {
 		dev_dbg(cxlds->dev,
 			"Device poison injection limit has been reached: %d\n",
-			MOCK_INJECT_DEV_MAX);
-		return false;
+			poison_inject_dev_max);
+		return -EBUSY;
 	}
 
 	for (int i = 0; i < MOCK_INJECT_TEST_MAX; i++) {
 		if (!mock_poison_list[i].cxlds) {
 			mock_poison_list[i].cxlds = cxlds;
 			mock_poison_list[i].dpa = dpa;
-			return true;
+			return 0;
 		}
 	}
 	dev_dbg(cxlds->dev,
 		"Mock test poison injection limit has been reached: %d\n",
 		MOCK_INJECT_TEST_MAX);
 
-	return false;
+	return -ENXIO;
 }
 
 static bool mock_poison_found(struct cxl_dev_state *cxlds, u64 dpa)
@@ -1179,10 +1180,8 @@ static int mock_inject_poison(struct cxl_dev_state *cxlds,
 		dev_dbg(cxlds->dev, "DPA: 0x%llx already poisoned\n", dpa);
 		return 0;
 	}
-	if (!mock_poison_add(cxlds, dpa))
-		return -ENXIO;
 
-	return 0;
+	return mock_poison_add(cxlds, dpa);
 }
 
 static bool mock_poison_del(struct cxl_dev_state *cxlds, u64 dpa)