RDMA/cma: Fix WARNING in res_to_rt

In the Linux kernel, the following vulnerability has been resolved:

RDMA/cma: Fix WARNING in res_to_rt

syzbot reported a WARN_ON(!res->dev) in res_to_rt() triggered via
addr_handler() during asynchronous address resolution:

"
WARNING: drivers/infiniband/core/restrack.c:138 at res_to_rt+0x1c4/0x230
CPU#1: kworker/u8:4/59
Modules linked in:
CPU: 1 UID: 0 PID: 59 Comm: kworker/u8:4 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: Google Compute Engine, BIOS Google 07/24/2026
Workqueue: ib_addr process_one_req
RIP: 0010:res_to_rt+0x1c4/0x230 drivers/infiniband/core/restrack.c:138
RSP: 0018:ffffc9000201f850 EFLAGS: 00010293
RAX: ffffffff88d00ce5 RBX: ffff88807f0fd4f8 RCX: ffff88801e6e0000
RDX: 0000000000000000 RSI: ffffffff8fd996f0 RDI: 0000000000000003
RBP: 0000000000000000 R08: ffff88801e6e0000 R09: 000000000000000a
R10: 0000000000000009 R11: 0000000000000000 R12: dffffc0000000000
R13: 1ffff1100fe1fa9f R14: 0000000000000000 R15: 0000000000000003
FS: 0000000000000000(0000) GS:ffff888125012000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00001d559c3d2000 CR3: 0000000077c4c000 CR4: 00000000003526f0
Call Trace:
<TASK>
rdma_restrack_add+0x5a/0x8a0 drivers/infiniband/core/restrack.c:236
addr_handler+0x41a/0x5a0 drivers/infiniband/core/cma.c:3534
process_one_req+0x2eb/0x540 drivers/infiniband/core/addr.c:624
process_one_work kernel/workqueue.c:3375 [inline]
process_scheduled_works+0xc4e/0x1630 kernel/workqueue.c:3458
worker_thread+0xa47/0xfb0 kernel/workqueue.c:3539
kthread+0x388/0x470 kernel/kthread.c:436
ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
</TASK>
"

In addr_handler(), cma_acquire_dev_by_src_ip() is called to populate
id_priv->cma_dev and bind the associated ib_device to id_priv->id.device.
If cma_acquire_dev_by_src_ip() returns an error (non-zero status), the ID
remains unassociated with any RDMA device.

Previously, rdma_restrack_add(&id_priv->res) was invoked unconditionally
even when cma_acquire_dev_by_src_ip() failed, passing a resource with a
NULL dev pointer and triggering the WARN_ON assertion in res_to_rt().

Fix this by only adding the resource to restrack when acquiring the device
succeeds.