atm: lanai: dont run lanai_dev_close if not open

lanai_dev_open() can fail. When it fail, lanai->base is unmapped and the
pci device is disabled. The caller, lanai_init_one(), then tries to run
atm_dev_deregister(). This will subsequently call lanai_dev_close() and
use the already released MMIO area.

To fix this issue, set the lanai->base to NULL if open fail,
and test the flag in lanai_dev_close().

[    8.324153] lanai: lanai_start() failed, err=19
[    8.324819] lanai(itf 0): shutting down interface
[    8.325211] BUG: unable to handle page fault for address: ffffc90000180024
[    8.325781] #PF: supervisor write access in kernel mode
[    8.326215] #PF: error_code(0x0002) - not-present page
[    8.326641] PGD 100000067 P4D 100000067 PUD 100139067 PMD 10013a067 PTE 0
[    8.327206] Oops: 0002 [#1] SMP KASAN NOPTI
[    8.327557] CPU: 0 PID: 95 Comm: modprobe Not tainted 5.11.0-rc7-00090-gdcc0b490 #12
[    8.328229] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.13.0-48-gd9c812dda519-...