mmc: sdhci: Fix vqmmc error setting

supply.vqmmc is used with the IS_ERR macro which means
the value must be valid or an error code.  NULL is
neither, so replace with ERR_PTR(-EINVAL).

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
diff --git a/drivers/mmc/host/sdhci.c b/drivers/mmc/host/sdhci.c
index a743d52..c2f4754 100644
--- a/drivers/mmc/host/sdhci.c
+++ b/drivers/mmc/host/sdhci.c
@@ -3096,7 +3096,7 @@
 		if (ret) {
 			pr_warn("%s: Failed to enable vqmmc regulator: %d\n",
 				mmc_hostname(mmc), ret);
-			mmc->supply.vqmmc = NULL;
+			mmc->supply.vqmmc = ERR_PTR(-EINVAL);
 		}
 	}