crypto: Remove stray PRIVATE in target_sources

fixup! crypto: Cleaning up PSA driver and core CMake logic

-PRIVATE doesn't work for target_sources

Signed-off-by: Frank Audun Kvamtrø <frank.kvamtro@nordicsemi.no>

subsys/nrf_security/src/drivers/zephyr/CMakeLists.txt

@@ -7,7 +7,6 @@
 # Add the RNG driver to the Oberon PSA core (if needed)
 if (PSA_NEED_NRF_RNG_ENTROPY_DRIVER)
   target_sources(${oberon_psa_core}
-    PRIVATE
       nrf_rng_entropy.c
   )
 endif()