sdhci: only reprogram retuning timer when flag is set

When the host->tuning_count is zero it means that the retuning is
disabled. This is checked on the first run of sdhci_execute_tuning()
by the if statement below:

	if (!(host->flags & SDHCI_NEEDS_RETUNING) && host->tuning_count &&
	    (host->tuning_mode == SDHCI_TUNING_MODE_1)) {

So only when tuning_count is non-zero it will set the host flag
SDHCI_USING_RETUNING_TIMER. The else statement is only for re-programming
the timer, which means that flag must be set. Because that is not checked
the else statement is executed in the first run when tuning_count is zero.

This was seen on a host controller which indicated SDHCI_TUNING_MODE_1 (0)
and tuning_count being zero. Suspect that (one of) these registers is not
properly set.

Signed-off-by: Arend van Spriel <arend@broadcom.com>
Acked-by: Ulf Hansson <ulf.hansson@linaro.org>
Reviewed-by: Aaron Lu <aaron.lu@intel.com>
Signed-off-by: Chris Ball <chris@printf.net>