lkdtm: fix memory leak of base

This case is supposed to read from a memory after it has been freed,
but we missed freeing base if the memory 'val' could not be allocated.

Signed-off-by: Sudip Mukherjee <sudip.mukherjee@codethink.co.uk>
Signed-off-by: Kees Cook <keescook@chromium.org>