Common: fixes discarded-qualifiers warnings (#2181)

Author: fam007e

src/common/impl/FFstrbuf.c

@@ -183,7 +183,7 @@ const char* ffStrbufAppendSUntilC(FFstrbuf* strbuf, const char* value, char unti
     if(value == NULL)
         return NULL;
 
-    char* end = strchr(value, until);
+    const char* end = strchr(value, until);
     if(end == NULL)
         ffStrbufAppendS(strbuf, value);
     else

src/common/impl/io_unix.c

@@ -23,7 +23,7 @@ static void createSubfolders(const char* fileName)
 {
     FF_STRBUF_AUTO_DESTROY path = ffStrbufCreate();
 
-    char *token = NULL;
+    const char *token = NULL;
     while((token = strchr(fileName, '/')) != NULL)
     {
         ffStrbufAppendNS(&path, (uint32_t)(token - fileName + 1), fileName);