lib/: Use non-empty compound literals

lib/: Use non-empty compound literals

While the empty one is more correct, {0} will also work, and will
likely silence diagnostics in old compiler versions.

Empty compound literals are only supported in GCC since commit
gcc.git 14cfa01755a6 (2022-08-25; "c: Support C2x empty initializer braces")

Reported-by: Serge Hallyn <serge@hallyn.com>
Signed-off-by: Alejandro Colomar <alx@kernel.org>