thunderbolt: Do not make DROM read success compulsory

BugLink: https://bugs.launchpad.net/bugs/1962349

The USB4 specification doesn't make any requirements that reading
a device router's DROM is needed for the operation of the device.

Other connection manager solutions don't necessarily read it or gate
the usability of the device on whether it was read.

So make failures when reading the DROM show warnings but not
fail the initialization of the router.

Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
(cherry picked from commit 6915812 linux-next)
Signed-off-by: You-Sheng Yang <vicamo.yang@canonical.com>
Signed-off-by: Timo Aaltonen <timo.aaltonen@canonical.com>

drivers/thunderbolt/switch.c

@@ -2724,10 +2724,8 @@ int tb_switch_add(struct tb_switch *sw)
 
 		/* read drom */
 		ret = tb_drom_read(sw);
-		if (ret) {
-			dev_err(&sw->dev, "reading DROM failed\n");
-			return ret;
-		}
+		if (ret)
+			dev_warn(&sw->dev, "reading DROM failed: %d\n", ret);
 		tb_sw_dbg(sw, "uid: %#llx\n", sw->uid);
 
 		tb_check_quirks(sw);