[CMakeLists.txt] The variable RVVM_SRC_DIR is set incorrectly

[HEYAHONG]

In CMakeList.txt, line 83 and line 84 set the same variable RVVM_SRC_DIR twice, causing some file paths (such as main.c, rvjit/rvjit.c) to be incorrect. It is recommended to add a new variable RVVM_SRC_UTIL_DIR for the src\util directory.