clk: mediatek: fix of_iomap memory leak

In the Linux kernel, the following vulnerability has been resolved: clk: mediatek: fix of_iomap memory leak Smatch reports: drivers/clk/mediatek/clk-mtk.c:583 mtk_clk_simple_probe() warn: 'base' from of_iomap() not released on lines: 496. This problem was also found in linux-next. In mtk_clk_simple_probe(), base is not released when handling errors if clk_data is not existed, which may cause a leak. So free_base should be added here to release base.