kernel: dynamic: add missing assert argument

Add a missing assert argument, fixes:

zephyrproject/zephyr/kernel/dynamic.c: In function 'dyn_cb':
zephyrproject/zephyr/include/zephyr/sys/__assert.h:44:52: warning:
	format '%p' expects a matching 'void *' argument [-Wformat=]

That started to break the build since:

d7846de5 assert: check format arguments for correctness

Signed-off-by: Fabio Baltieri <fabiobaltieri@google.com>