usb: gadget: composite: fix dereference after null check coverify warning

BugLink: https://bugs.launchpad.net/bugs/1826212

commit c526c62d upstream.

cdev->config is checked for null pointer at above code, so cdev->config
might be null, fix it by adding null pointer check.
Signed-off-by: Peter Chen <peter.chen@nxp.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

drivers/usb/gadget/composite.c

@@ -1819,6 +1819,8 @@ composite_setup(struct usb_gadget *gadget, const struct usb_ctrlrequest *ctrl)
 			break;
 
 		case USB_RECIP_ENDPOINT:
+			if (!cdev->config)
+				break;
 			endp = ((w_index & 0x80) >> 3) | (w_index & 0x0f);
 			list_for_each_entry(f, &cdev->config->functions, list) {
 				if (test_bit(endp, f->endpoints))