mmc: fix to assign to correct clock value when clock is enabling

When clock is enabling, it's assigned to 0 as mmc->clock.
Then it can't initialize any card.
Fix to assign to correct clock value as mmc->cfg->f_min or f_max.

Fixes: 9546eb92 ("mmc: fix the wrong disabling clock")
Signed-off-by: Jaehoon Chung <jh80.chung@samsung.com>
Tested-by: Guillaume GARDET <guillaume.gardet@free.fr>
Tested-by: Anand Moon <linux.amoon@gmail.com>
Tested-by: Stephen Warren <swarren@nvidia.com>