mmc: dw_mmc: cancel the CTO timer after a voltage switch

When running with the commit 03de1921 ("mmc: dw_mmc: introduce
timer for broken command transfer over scheme") I found this message
in the log:
  Unexpected command timeout, state 7

It turns out that we weren't properly cancelling the new CTO timer in
the case that a voltage switch was done.  Let's promote the cancel
into the dw_mci_cmd_interrupt() function to fix this.

Fixes: 03de1921 ("mmc: dw_mmc: introduce timer for broken command transfer over scheme")
Tested-by: Emil Renner Berthing <kernel@esmil.dk>
Reviewed-by: Shawn Lin <shawn.lin@rock-chips.com>
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>