libnvdimm, tools/testing/nvdimm: fix 'ars_status' output buffer sizing

Use the output length specified in the command to size the receive
buffer rather than the arbitrary 4K limit.

This bug was hiding the fact that the ndctl implementation of
ndctl_bus_cmd_new_ars_status() was not specifying an output buffer size.

Cc: <stable@vger.kernel.org>
Cc: Vishal Verma <vishal.l.verma@intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

drivers/nvdimm/bus.c

@@ -392,8 +392,8 @@ static const struct nd_cmd_desc __nd_cmd_bus_descs[] = {
 		.out_sizes = { 4, },
 	},
 	[ND_CMD_ARS_STATUS] = {
-		.out_num = 2,
-		.out_sizes = { 4, UINT_MAX, },
+		.out_num = 3,
+		.out_sizes = { 4, 4, UINT_MAX, },
 	},
 };
 
@@ -442,8 +442,8 @@ u32 nd_cmd_out_size(struct nvdimm *nvdimm, int cmd,
 		return in_field[1];
 	else if (nvdimm && cmd == ND_CMD_VENDOR && idx == 2)
 		return out_field[1];
-	else if (!nvdimm && cmd == ND_CMD_ARS_STATUS && idx == 1)
-		return ND_CMD_ARS_STATUS_MAX;
+	else if (!nvdimm && cmd == ND_CMD_ARS_STATUS && idx == 2)
+		return out_field[1] - 8;
 
 	return UINT_MAX;
 }