usb: xhci: Check for xhci->interrupters being allocated in xhci_mem_clearup()

If xhci_mem_init() fails, it calls into xhci_mem_cleanup() to mop
up the damage. If it fails early enough, before xhci->interrupters
is allocated but after xhci->max_interrupters has been set, which
happens in most (all?) cases, things get uglier, as xhci_mem_cleanup()
unconditionally derefences xhci->interrupters. With prejudice.

Gate the interrupt freeing loop with a check on xhci->interrupters
being non-NULL.

Found while debugging a DMA allocation issue that led the XHCI driver
on this exact path.

Fixes: c99b38c4 ("xhci: add support to allocate several interrupters")
Cc: Mathias Nyman <mathias.nyman@linux.intel.com>
Cc: Wesley Cheng <quic_wcheng@quicinc.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Cc: stable@vger.kernel.org # 6.8+
Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Link: https://lore.kernel.org/r/20240809124408.505786-2-mathias.nyman@linux.intel.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/host/xhci-mem.c

@@ -1872,7 +1872,7 @@ void xhci_mem_cleanup(struct xhci_hcd *xhci)
 
 	cancel_delayed_work_sync(&xhci->cmd_timer);
 
-	for (i = 0; i < xhci->max_interrupters; i++) {
+	for (i = 0; xhci->interrupters && i < xhci->max_interrupters; i++) {
 		if (xhci->interrupters[i]) {
 			xhci_remove_interrupter(xhci, xhci->interrupters[i]);
 			xhci_free_interrupter(xhci, xhci->interrupters[i]);