tests: kernel/smp: fixed missing 'z_' renaming
tests: kernel/smp: fixed missing 'z_' renaming

There was a missing 'z_' renaming to
z_is_thread_prevented_from_running which would have caused
sanitycheck to fail but it is not being built at the moment.
Fix this first.

Signed-off-by: Daniel Leung <d94e04d205b5962d7873a139ef298b03c1717f72@intel.com>

ldts/zephyr,Vudentz/zephyr,Vudentz/zephyr,galak/zephyr,nashif/zephyr,nashif/zephyr,Vudentz/zephyr,ldts/zephyr,nashif/zephyr,zephyrproject-rtos/zephyr,GiulianoFranchetto/zephyr,Vudentz/zephyr,finikorg/zephyr,ldts/zephyr,GiulianoFranchetto/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,finikorg/zephyr,Vudentz/zephyr,GiulianoFranchetto/zephyr,galak/zephyr,GiulianoFranchetto/zephyr,Vudentz/zephyr,galak/zephyr,finikorg/zephyr,GiulianoFranchetto/zephyr,ldts/zephyr,nashif/zephyr,nashif/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,ldts/zephyr