add missing const

Found with cppcheck

Signed-off-by: Rosen Penev <rosenp@gmail.com>

src/futils.cpp

@@ -195,7 +195,7 @@ size_t base64decode(const char* in, char* out, size_t out_size) {
 
 Protocol fileProtocol(const std::string& path) {
   Protocol result = pFile;
-  struct {
+  const struct {
     std::string name;
     Protocol prot;
     bool isUrl;  // path.size() > name.size()

src/olympusmn_int.cpp

@@ -1243,7 +1243,7 @@ std::ostream& OlympusMakerNote::print0x0201(std::ostream& os, const Value& value
 
   // 6 numbers: 0. Make, 1. Unknown, 2. Model, 3. Sub-model, 4-5. Unknown.
   // Only the Make, Model and Sub-model are used to determine the lens model
-  static struct {
+  static const struct {
     byte val[3];
     const char* label;
   } lensTypes[] = {
@@ -1397,7 +1397,7 @@ std::ostream& OlympusMakerNote::print0x0209(std::ostream& os, const Value& value
 std::ostream& OlympusMakerNote::printEq0x0301(std::ostream& os, const Value& value, const ExifData*) {
   // 6 numbers: 0. Make, 1. Unknown, 2. Model, 3. Sub-model, 4-5. Unknown.
   // Only the Make and Model are used to determine the extender model
-  static struct {
+  static const struct {
     byte val[2];
     const char* label;
   } extenderModels[] = {

src/sonymn_int.cpp

@@ -1864,7 +1864,7 @@ std::ostream& SonyMakerNote::printSony2FpFocusPosition2(std::ostream& os, const
     }
 
     // Ranges of models that do not support this tag
-    for (auto& m : {"DSC-", "Stellar"}) {
+    for (const auto& m : {"DSC-", "Stellar"}) {
       if (startsWith(model, m)) {
         os << N_("n/a");
         return os;