AAR: Fix build warning in last patch

Fix what happened to be just a build warning, but
surprisingly worked fine, at least with the compiler
and optimization level I used to test it.

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

src/HW_models/NHW_AAR.c

@@ -143,6 +143,7 @@ NSI_HW_EVENT(Timer_AAR, nhw_aar_timer_triggered, 50);
 
 static inline uint32_t read_3_bytes_value(const uint8_t *ptr) {
   uint32_t value = ptr[0] | (ptr[1] << 8) | (ptr[2] << 16);
+  return value;
 }
 
 /**