UBIFS: fix non-debug configuration build

Fix a brown paperbag bug introduced by me in the previous commit. I was
in hurry and forgot about the non-debug case completely.

Artem: amend the commit message and tweak the patch to preserve alignment.
       This made the patch a bit less readable, though.

Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@linux.intel.com>