[dxvk] Align length when clearing entire buffer

Buffer slices in DXVK are always aligned to at least
256 bytes, so this is safe. Fixes a regression leading
to GPU hangs on RADV.

src/dxvk/dxvk_context.cpp

@@ -230,6 +230,9 @@ namespace dxvk {
           uint32_t              value) {
     this->spillRenderPass();
     
+    if (length == buffer->info().size)
+      length = align(length, 4);
+    
     auto slice = buffer->subSlice(offset, length);
     
     m_cmd->cmdFillBuffer(