mmc: tmio: replace tmio_mmc_clk_stop() calls with tmio_mmc_set_clock()

tmio_mmc_clk_stop(host) is equivalent to tmio_mmc_set_clock(host, 0).
This replacement is needed for the next commit.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Reviewed-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>