The current code might succeed on the first allocation and fail on the
second. Separate the checks to avoid this problem.

Of course, free() will never fail and the chances that (when allocating
two small areas) one will succeed and one will fail are just as remote.
But this keeps coverity happy.

Reported-by: Coverity (CID: 131226)

Signed-off-by: Simon Glass <sjg@chromium.org>