mmc: sdhci-esdhc-imx: obtain the 'per' clock rate after its enablement

The I.MX SDHCI driver assumes that the frequency of the 'per' clock
can be obtained even on disabled clocks, which is not always the case.

According to 'clk_get_rate' documentation, it is only valid
once the clock source has been enabled.

Signed-off-by: Ciprian Costea <ciprianmarian.costea@oss.nxp.com>
Reviewed-by: Haibo Chen <haibo.chen@nxp.com>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Link: https://lore.kernel.org/r/20240708121018.246476-3-ciprianmarian.costea@oss.nxp.com


Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>