mmc: core: duplicated trial with same freq in mmc_rescan_try_freq()

mmc_rescan_try_freq() tries to init two times with the last frequency.
For example, if host->f_min is 400KHz, we see the message below:

mmc1: mmc_rescan_try_freq: trying to init card at 400000 Hz
mmc1: mmc_rescan_try_freq: trying to init card at 400000 Hz

Andy Ross says that he didn't try this code on a board with an f_min
that exactly matches one of the table entries, which explains why the
bug wasn't detected.

Signed-off-by: Jaehoon Chung <jh80.chung@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Cc: Andy Ross <andy.ross@windriver.com>
Signed-off-by: Chris Ball <cjb@laptop.org>