Fix typo ("x86_64" -> "X86_64")

...introduced with 2d2294fb "Add x64 Windows
here, too".  As reported by Richard Webb at
<https://lists.freedesktop.org/archives/libreoffice/2018-March/079870.html>
"Re: Manifest.xml for 64bit LO".

Change-Id: I1681908012e73e520bebd79b8149788358ea49a3
Reviewed-on: https://gerrit.libreoffice.org/51946Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>

desktop/source/deployment/misc/dp_platform.cxx

@@ -77,7 +77,7 @@ namespace
         else if (token == "windows_x86")
             ret = checkOSandCPU("Windows", "x86");
         else if (token == "windows_x86_64")
-            ret = checkOSandCPU("Windows", "x86_64");
+            ret = checkOSandCPU("Windows", "X86_64");
         else if (token == "solaris_sparc")
             ret = checkOSandCPU("Solaris", "SPARC");
         else if (token == "solaris_sparc64")