CVE-2026-98519: drm/amdgpu: Fix runtime PM leak in amdgpu_debugfs_test_ib_show()

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

drm/amdgpu: Fix runtime PM leak in amdgpudebugfstestibshow()

amdgpudebugfstestibshow() resumes the device with pmruntimegetsync() before taking the reset domain semaphore with downwritekillable(). If the write lock acquisition is interrupted, the function returns without calling pmruntimeputautosuspend(), leaking the runtime PM reference acquired for the device and keeping the GPU awake.

Drop the runtime PM reference on the interrupted downwritekillable() error path before returning.

(cherry picked from commit ec30a576c2d4c0364549e6c04218f50704ef56c8)