drm/radeon: fix memory leak in radeon_ring_restore() on lock failure

In the Linux kernel, the following vulnerability has been resolved: drm/radeon: fix memory leak in radeon_ring_restore() on lock failure radeon_ring_restore() takes ownership of the data buffer allocated by radeon_ring_backup(). The caller (radeon_gpu_reset()) only frees it in the non-restore branch; in the restore branch it relies on radeon_ring_restore() to free it. If radeon_ring_lock() fails, the function returned early without calling kvfree(data), leaking the ring backup buffer on every GPU reset that fails at the lock stage. During repeated GPU resets this causes cumulative kernel memory exhaustion. Free data before returning the error.