usb: gadget: Check bmAttributes only if configuration is valid

If the USB configuration is not valid, then avoid checking for
bmAttributes to prevent null pointer deference.

Cc: stable <stable@kernel.org>
Fixes: 40e89ff ("usb: gadget: Set self-powered based on MaxPower and bmAttributes")
Signed-off-by: Prashanth K <prashanth.k@oss.qualcomm.com>
Link: https://lore.kernel.org/r/20250224085604.417327-1-prashanth.k@oss.qualcomm.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: Prashanth K

drivers/usb/gadget/composite.c

@@ -1051,7 +1051,7 @@ static int set_config(struct usb_composite_dev *cdev,
 		usb_gadget_set_remote_wakeup(gadget, 0);
 done:
 	if (power > USB_SELF_POWER_VBUS_MAX_DRAW ||
-	    !(c->bmAttributes & USB_CONFIG_ATT_SELFPOWER))
+	    (c && !(c->bmAttributes & USB_CONFIG_ATT_SELFPOWER)))
 		usb_gadget_clear_selfpowered(gadget);
 	else
 		usb_gadget_set_selfpowered(gadget);