mmc: dw_mmc: display the clock message only one time when card is polling

When card is polling (broken-cd), there is a spamming messge related to
clock.
After applied this patch, display the message only one time at boot
time. It's enough to check which clock values is used.
Also prevent to display the spamming message.

Signed-off-by: Jaehoon Chung <jh80.chung@samsung.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>