dma-api debugfs directory is not created since debugfs is not initialized

[Corentin Labbe]

Hello

I try to debug some DMA problem on next-20210427, and so I have enabled CONFIG_DMA_API_DEBUG=y.
But the dma-api directory does show up in debugfs, but lot of other directory exists in it.

After debugging it seems due to commit 56348560d495 ("debugfs: do not attempt to create a new file before the filesystem is initalized")
Reverting the commit permit to "dma-api" debugfs to be found. (but seems not the right way to fix it).

Regards