drm/xe: Fix error cleanup in xe_exec_queue_create_ioctl()

Two error handling issues exist in xe_exec_queue_create_ioctl():

1. When xe_hw_engine_group_add_exec_queue() fails, the error path jumps
to put_exec_queue which skips xe_exec_queue_kill(). If the VM is in
preempt fence mode, xe_vm_add_compute_exec_queue() has already added
the queue to the VM's compute exec queue list. Skipping the kill
leaves the queue on that list, leading to a dangling pointer after
the queue is freed.

2. When xa_alloc() fails after xe_hw_engine_group_add_exec_queue() has
succeeded, the error path does not call
xe_hw_engine_group_del_exec_queue() to remove the queue from the hw
engine group list. The queue is then freed while still linked into
the hw engine group, causing a use-after-free.

Fix both by:
- Changing the xe_hw_engine_group_add_exec_queue() failure path to jump
to kill_exec_queue so that xe_exec_queue_kill() properly removes the
queue from the VM's compute list.
- Adding a del_hw_engine_group label before kill_exec_queue for the
xa_alloc() failure path, which removes the queue from the hw engine
group before proceeding with the rest of the cleanup.

Fixes: 7970cb36966c ("'drm/xe/hw_engine_group: Register hw engine group's exec queues")
Cc: Francois Dugast <francois.dugast@intel.com>
Cc: Matthew Brost <matthew.brost@intel.com>
Cc: Niranjana Vishwanathapura <niranjana.vishwanathapura@intel.com>
Assisted-by: Claude:claude-opus-4.6
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Link: https://patch.msgid.link/20260408020647.3397933-1-shuicheng.lin@intel.com
Signed-off-by: Shuicheng Lin <shuicheng.lin@intel.com>
(cherry picked from commit 37c831f401746a45d510b312b0ed7a77b1e06ec8)
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>