mmc: fix the wrong disabling clock

When power is off, clock is not disabling.
Because it's passed to 1, mmc->clock should be set to f_min value.
Some drivers can't initialize the eMMC/SD card with current status.

This patch is to fix the disabling clock value to 0.

Fixes: 2e7410d7 ("mmc: disable the mmc clock during power off")

Signed-off-by: Jaehoon Chung <jh80.chung@samsung.com>
Reviewed-by: Jean-Jacques Hiblot <jjhiblot@ti.com>
Tested-by: Guillaume GARDET <guillaume.gardet@free.fr>
Tested-by: Anand Moon <linux.amoon@gmail.com>