mmc: sdhci-s3c: fix the wrong number of max bus clocks

We can use up to four bus-clocks; but on module remove, we didn't
disable the fourth bus clock.

Signed-off-by: Jaehoon Chung <jh80.chung@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Chris Ball <cjb@laptop.org>