xhci: solve a double free problem while doing s4

when system is doing s4, the process of xhci_resume may be as below:
1、xhci_mem_cleanup
2、xhci_init->xhci_mem_init->xhci_mem_cleanup(when memory is not enough).
xhci_mem_cleanup will be executed twice when system is out of memory.
xhci->port_caps is freed in xhci_mem_cleanup,but it isn't set to NULL.
It will be freed twice when xhci_mem_cleanup is called the second time.

We got following bug when system resumes from s4:

kernel BUG at mm/slub.c:309!
Internal error: Oops - BUG: 0 [#1] PREEMPT SMP
CPU: 0 PID: 5929 Tainted: G S   W   5.4.96-arm64-desktop #1
pc : __slab_free+0x5c/0x424
lr : kfree+0x30c/0x32c

Call trace:
 __slab_free+0x5c/0x424
 kfree+0x30c/0x32c
 xhci_mem_cleanup+0x394/0x3cc
 xhci_mem_init+0x9ac/0x1070
 xhci_init+0x8c/0x1d0
 xhci_resume+0x1cc/0x5fc
 xhci_plat_resume+0x64/0x70
 platform_pm_thaw+0x28/0x60
 dpm_run_callback+0x54/0x24c
 device_resume+0xd0/0x200
 async_resume+0x24/0x60
 async_run_entry_fn+0x44/0x110
 process_one_work+0x1f0/0x490
 worker_thread+0x5c/0x450
 kthread+0x158/0x160
 ret_from_fork+0x10/0x24

Original patch that caused this issue was backported to 4.4 stable,
so this should be backported to 4.4 stabe as well.

Fixes: cf0ee7c6 ("xhci: Fix memory leak when caching protocol extended capability PSI tables - take 2")
Cc: stable@vger.kernel.org # v4.4+
Signed-off-by: Jiantao Zhang <water.zhangjiantao@huawei.com>
Signed-off-by: Tao Xue <xuetao09@huawei.com>
Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Link: https://lore.kernel.org/r/20210617150354.1512157-5-mathias.nyman@linux.intel.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/host/xhci-mem.c

@@ -1924,6 +1924,7 @@ void xhci_mem_cleanup(struct xhci_hcd *xhci)
 	xhci->hw_ports = NULL;
 	xhci->rh_bw = NULL;
 	xhci->ext_caps = NULL;
+	xhci->port_caps = NULL;
 
 	xhci->page_size = 0;
 	xhci->page_shift = 0;