mmc: Set clock when reverting to safe bus mode

Set MMC clock when reverting to safe bus mode and speed
in case current MMC mode fails. Otherwise, trying out
the other modes may fail as well.

Reviewed-by: Marek Vasut <marek.vasut+renesas@mailbox.org>
Signed-off-by: Valentine Barshak <valentine.barshak@cogentembedded.com>
[hp: fallback to legacy_speed]
Signed-off-by: Hai Pham <hai.pham.ud@renesas.com>
Reviewed-by: Peng Fan <peng.fan@nxp.com>