mmc: sh_mobile_sdhi: remove superfluous check in init_tuning

The function will only be available if SDR104 was detected in probe,
so no need to check in the function itself again.

Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>