cmake/nuttx_kconfig.cmake: fixed the correct .config path in the build folder

Fixing the correct .config path during the setconfig process.

changed ${NUTTX_DIR} -> ${CMAKE_BINARY_DIR}

see apache#13175 (comment)

Author: simbit18

cmake/nuttx_kconfig.cmake

@@ -160,6 +160,6 @@ endfunction()
 function(nuttx_setconfig)
   execute_process(
     COMMAND ${CMAKE_COMMAND} -E env ${KCONFIG_ENV} setconfig ${ARGN}
-    WORKING_DIRECTORY ${NUTTX_DIR}
+    WORKING_DIRECTORY ${CMAKE_BINARY_DIR}
     OUTPUT_QUIET ERROR_QUIET)
 endfunction()