mkfs-ubifs: fix inclusion of uuid.h

mkfs-ubifs: fix inclusion of uuid.h

The include directory exported by uuid.pc is */include/uuid, so uuid.h
must be included without any directory in the path. This usually works
out because uuid is installed in the normal prefix, so the parent
directory of what uuid has as include dir ends up in the include path
anyway. In case one uses a custom uuid outside of the regular include
path this breaks.

Signed-off-by: Rolf Eike Beer <eb@emlix.com>
Signed-off-by: David Oberhollenzer <david.oberhollenzer@sigma-star.at>