mmc: dw_mmc: Increase cmd11 timeout to 500ms

Although the cmd11 interrupt should come within 2ms, that's a very
short time.  Let's increase the timeout to be really sure that we
don't get an accidnetal timeout.  One case in particular this is
useful is if you've got a serial console and printk in just the right
places.  Under that scenario I've seen delays of up to 130ms before
the interrupt fired.

CMD11 is only sent during card insertion, so this extra timeout
shouldn't be terrible.

Fixes: 5c935165 ("mmc: dw_mmc: Add a timeout for sending CMD11")
Signed-off-by: Doug Anderson <dianders@chromium.org>
Signed-off-by: Jaehoon Chung <jh80.chung@samsung.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>