kernel: kheap: workaround for Percepio's TraceRecorder kludge

In .../modules/debug/percepio/TraceRecorder/kernelports/Zephyr/include/\
tracing_tracerecorder.h there is a concealed non-parameterized direct
reference to a local variable that is no longer in scope. Provide a dummy
stub for compilation to succeed until that module's layering violation is
fixed, after which this could be reverted.

Signed-off-by: Nicolas Pitre <npitre@baylibre.com>