formatutils: ensure we dont leak name ptr (#2)

store format name in a std::string and free the char ptr to ensure we
dont leak on each call to drmGetFormatName.

src/utils/FormatUtils.cpp

@@ -4,5 +4,7 @@
 
 std::string fourccToName(uint32_t drmFormat) {
     auto        fmt  = drmGetFormatName(drmFormat);
-    return fmt ? fmt : "unknown";
+    std::string name = fmt ? fmt : "unknown";
+    free(fmt);
+    return name;
 }