i3c: Add NULL pointer check in i3c_master_queue_ibi()

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

i3c: Add NULL pointer check in i3c_master_queue_ibi()

The I3C master driver may receive an IBI from a target device that has not

been probed yet. In such cases, the master calls `i3c_master_queue_ibi()`

to queue an IBI work task, leading to "Unable to handle kernel read from

unreadable memory" and resulting in a kernel panic.

Typical IBI handling flow:

1. The I3C master scans target devices and probes their respective drivers.

2. The target device driver calls `i3c_device_request_ibi()` to enable IBI

and assigns `dev->ibi = ibi`.

3. The I3C master receives an IBI from the target device and calls

`i3c_master_queue_ibi()` to queue the target device driver’s IBI

handler task.

However, since target device events are asynchronous to the I3C probe

sequence, step 3 may occur before step 2, causing `dev->ibi` to be `NULL`,

leading to a kernel panic.

Add a NULL pointer check in `i3c_master_queue_ibi()` to prevent accessing

an uninitialized `dev->ibi`, ensuring stability.