mmc: sdhci-esdhc: break out early if clock is 0

mmc: sdhci-esdhc: break out early if clock is 0

commit 74f330bceaa7b88d06062e1cac3d519a3dfc041e upstream.

Since commit 30832ab56 ("mmc: sdhci: Always pass clock request value
zero to set_clock host op") was merged, esdhc_set_clock starts hitting
"if (clock == 0)" where ESDHC_SYSTEM_CONTROL has been operated.  This
causes SDHCI card-detection function being broken.  Fix the regression
by moving "if (clock == 0)" above ESDHC_SYSTEM_CONTROL operation.

Signed-off-by: Shawn Guo <shawn.guo@linaro.org>
Signed-off-by: Chris Ball <cjb@laptop.org>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>