mmc: dw_mmc: Remove dw_mci_start_request wrapper and rename core function

mmc: dw_mmc: Remove dw_mci_start_request wrapper and rename core function

The function dw_mci_start_request() was just a thin wrapper around
__dw_mci_start_request(). Since it serves almost no functional purpose,
remove the wrapper to simplify the code flow.

Consequently, rename __dw_mci_start_request() to dw_mci_start_request()
so that the core implementation uses the primary name.

Signed-off-by: Shawn Lin <shawn.lin@rock-chips.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>