Add va_end and returns to variadic functions (#950)

src/libultra_boot_O2/sprintf.c

@@ -21,5 +21,8 @@ s32 sprintf(char* dst, const char* fmt, ...) {
     if (ret > -1) {
         dst[ret] = 0;
     }
+
+    va_end(args);
+
     return ret;
 }