mmc: sdhci: Simplify use of tuning timer

The tuning timer is always used if the tuning mode
is 1 and there is a tuning count, irrespective of
whether this is the first call, or any subsequent
call. Consequently the logic to start the timer
can be simplified.

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Reviewed-by: Aaron Lu <aaron.lu@intel.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>