mmc: sdhci-xenon: fix PHY init clock stability

Each time SD/mmc phy is initialized, at times, in some of
the attempts, phy fails to completes its initialization
which results into timeout error. Per the HW spec, it is
a pre-requisite to ensure a stable SD clock before a phy
initialization is attempted.

Fixes: 06c8b667

 ("mmc: sdhci-xenon: Add support to PHYs of Marvell Xenon SDHC")
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Cc: stable@vger.kernel.org
Signed-off-by: Elad Nachman <enachman@marvell.com>
Link: https://lore.kernel.org/r/20240222200930.1277665-1-enachman@marvell.com
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>