usb: typec: ucsi: displayport: Current CAM OOB index fixup

Update ucsi_displayport_enter() to return invalid error when the PPM reports an current alternate mode greater than or equal to UCSI_MAX_ALTMODES. While here, remove 0xff current cam assignment on failed GET_CURRENT_CAM response.

---
Changes in v2
- added fixes tag and CC stable

Original patch didn't incorporate reviewer feedback. This is a fixup to be amended to:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=04cec690b1fd9d1c4c314b91a10d8c68a3acfe18

 drivers/usb/typec/ucsi/displayport.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

index 8d2032d0762c..572da7bbd29c 100644
@@ -71,11 +71,14 @@ static int ucsi_displayport_enter(struct typec_altmode *alt, u32 *vdo)
 	if (ret < 0) {
 		if (ucsi->version > 0x0100)
 			goto err_unlock;
-		cur = 0xff;
 	}
 
-	if (cur < UCSI_MAX_ALTMODES) {
-		ret = dp->con->port_altmode[cur] == alt ? 0 : -EBUSY;
+	if (cur != 0xff) {
+		if (cur < UCSI_MAX_ALTMODES)
+			ret = dp->con->port_altmode[cur] == alt ? 0 : -EBUSY;
+		else
+			ret = -EINVAL;
+
 		goto err_unlock;
 	}
 

base-commit: 600334ef2f29b975485ce062a81fcfa00bd3ef45

2.55.0.1082.g2b9226bbc0-goog