mmc: dw_mmc: properly address command completion in dwmci_control_clken()

mmc: dw_mmc: properly address command completion in dwmci_control_clken()

The current implementation polls for the DWMCI_CMD register, for the
DWMCI_CMD_START bit to turn off, which indicates that the command has
been completed. The problem with this approach is that it doesn't
address the DWMCI_INTMSK_CDONE bit in the interrupt register,
DWMCI_RINTSTS. As a result, subsequent commands result in timeout errors.

Re-implement the waiting logic by polling for said interrupt status bit
and setting it low if raised.

Signed-off-by: Kaustabh Chakraborty <kauschluss@disroot.org>
Signed-off-by: Peng Fan <peng.fan@nxp.com>