plugin-manager: protect mm_plugin_{major,minor}_version

This patch makes declarations bind to definitions within the same module
to prevent the potential ambiguity if referenced directly.

AddressSanitizer think they violated one definition rule, although
those symbols are accessed by address through their modules and do
not depend on the order of the libararies loaded.

plugins/simtech/mm-plugin-simtech.c

@@ -27,8 +27,8 @@
 
 G_DEFINE_TYPE (MMPluginSimtech, mm_plugin_simtech, MM_TYPE_PLUGIN)
 
-int mm_plugin_major_version = MM_PLUGIN_MAJOR_VERSION;
-int mm_plugin_minor_version = MM_PLUGIN_MINOR_VERSION;
+MM_PLUGIN_DEFINE_MAJOR_VERSION
+MM_PLUGIN_DEFINE_MINOR_VERSION
 
 /*****************************************************************************/