drm/nouveau/bios: log if auxch accesses fail, also return 0x00 from rd when it does

Logging at trace level, rather than as en error, as it seems conceivable
that failure could be normal under certain circumstances (new bios,
older sink that doesn't support a particular DPCD address)
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>

drivers/gpu/drm/nouveau/core/subdev/bios/init.c

@@ -278,7 +278,7 @@ init_wri2cr(struct nvbios_init *init, u8 index, u8 addr, u8 reg, u8 val)
 	return -ENODEV;
 }
 
-static int
+static u8
 init_rdauxr(struct nvbios_init *init, u32 addr)
 {
 	struct nouveau_i2c_port *port = init_i2c(init, -2);
@@ -286,20 +286,24 @@ init_rdauxr(struct nvbios_init *init, u32 addr)
 
 	if (port && init_exec(init)) {
 		int ret = nv_rdaux(port, addr, &data, 1);
-		if (ret)
-			return ret;
+		if (ret == 0)
 			return data;
+		trace("auxch read failed with %d\n", ret);
 	}
 
-	return -ENODEV;
+	return 0x00;
 }
 
 static int
 init_wrauxr(struct nvbios_init *init, u32 addr, u8 data)
 {
 	struct nouveau_i2c_port *port = init_i2c(init, -2);
-	if (port && init_exec(init))
-		return nv_wraux(port, addr, &data, 1);
+	if (port && init_exec(init)) {
+		int ret = nv_wraux(port, addr, &data, 1);
+		if (ret)
+			trace("auxch write failed with %d\n", ret);
+		return ret;
+	}
 	return -ENODEV;
 }