mmc: core: Allow invalid regulator in mmc_regulator_set_ocr()

Basically all host drivers use code like this:

if (!IS_ERR(mmc->supply.vmmc))
	mmc_regulator_set_ocr(mmc, mmc->supply.vmmc, 0)

Move the IS_ERR() check to mmc_regulator_set_ocr() to simplify host driver
code.
Suggested-by: Ulf Hansson <ulf.hansson@linaro.org>
Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Link: https://lore.kernel.org/r/0c1e7440-f4bc-b48a-137f-58b75ac98550@gmail.comSigned-off-by: Ulf Hansson <ulf.hansson@linaro.org>

drivers/mmc/core/regulator.c

@@ -110,6 +110,9 @@ int mmc_regulator_set_ocr(struct mmc_host *mmc,
 	int			result = 0;
 	int			min_uV, max_uV;
 
+	if (IS_ERR(supply))
+		return 0;
+
 	if (vdd_bit) {
 		mmc_ocrbitnum_to_vdd(vdd_bit, &min_uV, &max_uV);