[media] coda: fix double call to debugfs_remove

In coda_free_aux_buf() call debugfs_remove only if buffer entry
is valid (and therfore dentry is valid), double protect by
invalidating dentry value.

Fixes erroneous prematurely dealloc of debugfs caused by
incorrect reference count incrementing.

Signed-off-by: Peter Seiderer <ps.report@gmx.net>
Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: Kamil Debski <k.debski@samsung.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>

drivers/media/platform/coda/coda-common.c

@@ -1215,8 +1215,9 @@ void coda_free_aux_buf(struct coda_dev *dev,
 				  buf->vaddr, buf->paddr);
 		buf->vaddr = NULL;
 		buf->size = 0;
+		debugfs_remove(buf->dentry);
+		buf->dentry = NULL;
 	}
-	debugfs_remove(buf->dentry);
 }
 
 static int coda_start_streaming(struct vb2_queue *q, unsigned int count)