api,compat: fix warnings during doc build

We just move the MM_DISABLE_DEPRECATED check to after the
MM_DEPRECATED symbol definition, because gtkdoc-scan gets pretty
confused, likely due to the symbol ending with the "_DEPRECATED"
suffix.

Fixes https://gitlab.freedesktop.org/mobile-broadband/ModemManager/issues/91

include/ModemManager-compat.h

@@ -22,8 +22,6 @@
 
 #include <ModemManager-enums.h>
 
-#ifndef MM_DISABLE_DEPRECATED
-
 /**
  * SECTION:mm-compat
  * @title: API break replacements
@@ -41,6 +39,8 @@
 # define MM_DEPRECATED
 #endif
 
+#ifndef MM_DISABLE_DEPRECATED
+
 /* The following type exists just so that we can get deprecation warnings */
 MM_DEPRECATED
 typedef int MMModemBandDeprecated;