uboot-envtools: fix build if ubi volume support is disabled

Insert a missing #ifdef UBI around the use of libubi_close().
As the preceding if (libubi) will never be true on non-UBI builds,
compiling only failed when disabling optimization.

Also rebase patch to latest u-boot.git HEAD.

Signed-off-by: Daniel Golle <daniel@makrotopia.org>

SVN-Revision: 41313