The Kona SDHCI block requires a clock that must be specified in the
device tree.  Update the documentation to reflect this requirement.
Signed-off-by: NTim Kryger <tim.kryger@linaro.org>
Reviewed-by: NMatt Porter <matt.porter@linaro.org>
Signed-off-by: NChristian Daudt <bcm@fixthebug.org>