UBIFS: do not change debugfs file position

This patch is a tiny improvement which removes few bytes of code.
UBIFS debugfs files are non-seekable and the file position is ignored,
so do not increase it in the write handler.

Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
diff --git a/fs/ubifs/debug.c b/fs/ubifs/debug.c
index 4062ec6..f7515bd 100644
--- a/fs/ubifs/debug.c
+++ b/fs/ubifs/debug.c
@@ -2828,7 +2828,6 @@
 	} else
 		return -EINVAL;
 
-	*ppos += count;
 	return count;
 }