mmc: sdhci-s3c: add spin_unlock_irq() before calling clk_round_rate

Before calling clk_round_rate(), put the spin_unlock_irq() in
sdhci_s3c_consider_clock() function.

Signed-off-by: Jaehoon Chung <jh80.chung@samsung.com>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>