mmc: sdhci-of-aspeed: Drop redundant assignment to host->clock

host->clock is already managed by sdhci_set_ios().

Suggested-by: Ulf Hansson <ulf.hansson@linaro.org>
Signed-off-by: Andrew Jeffery <andrew@aj.id.au>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>