sdhci : recompute timeout_clk when needed

when SDHCI_QUIRK_DATA_TIMEOUT_USES_SDCLK is set, timeout_clk is sdclk.
We need to update it when we change sdclk in sdhci_set_clock.
This allow to have a more precisse timeout and max_busy_timeout. This
can help for command that need a big busy wait (erase, ...).

Signed-off-by: Matthieu CASTET <matthieu.castet@parrot.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>