mmc: dw_mmc: fix the debug message for checking card's present

If display the debug message, this message should be spamming.
If flags is maintained the previous value, didn't display the debug
message.

Signed-off-by: Jaehoon Chung <jh80.chung@samsung.com>
Tested-by: Heiko Stuebner <heiko@sntech.de>
Reviewed-by: Shawn Lin <shawn.lin@rock-chips.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>