fix "Wrap opencl-only functions in appropriate ifdef."

06287185
(loplugin:unreffun fix) caused:
  'undefined reference to `sc::FormulaGroupInterpreter::msInstance'
when building with --disable-opencl.

(It appears I didn't check whether my build had fully completed before pushing.)

Change-Id: I948205867985c7722662d673e95d5639bc9d9bcc

sc/source/core/tool/formulagroup.cxx

@@ -532,10 +532,12 @@ typedef void (*__fillOpenCLInfo)(OpenclPlatformInfo*, size_t);
 typedef bool (*__switchOpenClDevice)(const OUString*, bool, bool);
 typedef void (*__getOpenCLDeviceInfo)(size_t*, size_t*);
 
+#endif
 #endif
 
 FormulaGroupInterpreter *FormulaGroupInterpreter::msInstance = NULL;
 
+#if HAVE_FEATURE_OPENCL
 #ifndef DISABLE_DYNLOADING
 
 osl::Module* getOpenCLModule()