mmc: dw_mmc: Extract divider update to a separate function

mmc: dw_mmc: Extract divider update to a separate function

Extract the clock divider update into dwmci_update_div() function. It's
a procedure recommended in TRM, so it's better to keep it in a dedicated
function to make the code clearer.

While at it also extract the clock control code into a separate routine
to avoid code duplication in dwmci_setup_bus().

No functional change.

Signed-off-by: Sam Protsenko <semen.protsenko@linaro.org>
Signed-off-by: Minkyu Kang <mk7.kang@samsung.com>