cmake: kconfig: rename variable to correct naming convention

Variables used only internally in the module should have lowercase
names.

Signed-off-by: Richard Hughes <rhughes@xilinx.com>

cmake/modules/kconfig.cmake

@@ -382,13 +382,13 @@ if(CREATE_NEW_DOTCONFIG)
 endif()
 
 # Read out the list of 'Kconfig' sources that were used by the engine.
-file(STRINGS ${PARSED_KCONFIG_SOURCES_TXT} PARSED_KCONFIG_SOURCES_LIST ENCODING UTF-8)
+file(STRINGS ${PARSED_KCONFIG_SOURCES_TXT} parsed_kconfig_sources_list ENCODING UTF-8)
 
 # Force CMAKE configure when the Kconfig sources or configuration files changes.
 foreach(kconfig_input
     ${merge_config_files}
     ${DOTCONFIG}
-    ${PARSED_KCONFIG_SOURCES_LIST}
+    ${parsed_kconfig_sources_list}
     )
   set_property(DIRECTORY APPEND PROPERTY CMAKE_CONFIGURE_DEPENDS ${kconfig_input})
 endforeach()