scsi: scsi_debug: Fix a memory leak

The sdebug_q_arr pointer must be freed when the module is unloaded.

$ cat /sys/kernel/debug/kmemleak
unreferenced object 0xffff888e1cfb0000 (size 4096):
  comm "modprobe", pid 165555, jiffies 4325987516 (age 685.194s)
  hex dump (first 32 bytes):
    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
  backtrace:
    [<00000000458f4f5d>] 0xffffffffc06702d9
    [<000000003edc4b1f>] do_one_initcall+0xe9/0x57d
    [<00000000da7d518c>] do_init_module+0x1d1/0x6f0
    [<000000009a6a9248>] load_module+0x36bd/0x4f50
    [<00000000ddb0c3ce>] __do_sys_init_module+0x1db/0x260
    [<000000009532db57>] do_syscall_64+0xa5/0x420
    [<000000002916b13d>] entry_SYSCALL_64_after_hwframe+0x6a/0xdf

Fixes: 87c715d ("scsi: scsi_debug: Add per_host_store option")
Link: https://lore.kernel.org/r/20210208111734.34034-1-mlombard@redhat.com
Acked-by: Douglas Gilbert <dgilbert@interlog.com>
Signed-off-by: Maurizio Lombardi <mlombard@redhat.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/scsi_debug.c

@@ -6881,6 +6881,7 @@ static void __exit scsi_debug_exit(void)
 
 	sdebug_erase_all_stores(false);
 	xa_destroy(per_store_ap);
+	kfree(sdebug_q_arr);
 }
 
 device_initcall(scsi_debug_init);