mmc: bcm2835: set SDHCI_QUIRK_DATA_TIMEOUT_USES_SDCLK

SDHCI_QUIRK_DATA_TIMEOUT_USES_SDCLK does basically the same as
implementing struct sdhci_ops .get_timeout_clock, so simply set that
quirk and remove the custom code to simplify the driver.

Reported-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Stephen Warren <swarren@wwwdotorg.org>
Signed-off-by: Chris Ball <cjb@laptop.org>