clk: mediatek: clk-mt8173: Unmap region obtained by of_iomap

Free memory mapping if init is not successful.

Signed-off-by: Arvind Yadav <arvind.yadav.cs@gmail.com>
Reviewed-by: James Liao <jamesjj.liao@mediatek.com>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>