mmc: sdhci: calculate timeout_clk conditionally in sdhci_add_host

The timeout_clk calculation code in sdhci_add_host is meaningless for
SDHCI_QUIRK_DATA_TIMEOUT_USES_SDCLK.
So only execute them with no SDHCI_QUIRK_DATA_TIMEOUT_USES_SDCLK set.

Signed-off-by: Dong Aisheng <b29396@freescale.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>