drivers: clock_control_nrf: Fix link error with ASAN and no SHELL

When ASAN is used cmd_status is kept, but it cannot be linked
as the shell module is not present, this prevents ASAN
being used with the nrf52_bsim.
Fix it by conditionally compiling this code only if the shell is
being used.

Signed-off-by: Alberto Escolar Piedras <alberto.escolar.piedras@nordicsemi.no>