drm/amdgpu/sdma4: replace BUG_ON with WARN_ON in fence emission

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

drm/amdgpu/sdma4: replace BUG_ON with WARN_ON in fence emission

sdma_v4_0_ring_emit_fence() contains two BUG_ON(addr & 0x3) assertions

that verify fence writeback addresses are dword-aligned. These

assertions can be reached from unprivileged userspace via crafted

DRM_IOCTL_AMDGPU_CS submissions, causing a fatal kernel panic in a

scheduler worker thread.

Replace both BUG_ON() calls with WARN_ON() to log the condition without

crashing the kernel. A misaligned fence address at this point indicates

a driver bug, but crashing the kernel is never the correct response when

the assertion is reachable from userspace.

The CS IOCTL path is the correct place to filter invalid submissions;

the ring emission callback is too late to do anything about it.

(cherry picked from commit b90250bd933afd1ba94d86d6b13821997b22b18e)