kernel: Fix usage of CONFIG_SYS_CLOCK_EXISTS

When compiling the kernel with CONFIG_SYS_CLOCK_TICKS_PER_SEC=0,
the CONFIG_SYS_CLOCK_EXISTS internal variable is unset.
This completely disables timer handling in the kernel, but a couple of
spots missed the required conditional compilation.

Signed-off-by: Carles Cufi <carles.cufi@nordicsemi.no>
4 files changed