mmc: sdhci: Don't ignore regulator_enable() return value

Fixes:
/git/arm-soc/drivers/mmc/host/sdhci.c: In function 'sdhci_add_host':
/git/arm-soc/drivers/mmc/host/sdhci.c:2910:19: warning: ignoring
return value of 'regulator_enable', declared with attribute
warn_unused_result [-Wunused-result]
Reported-by: NArnd Bergmann <arnd@arndb.de>
Signed-off-by: NChris Ball <cjb@laptop.org>

drivers/mmc/host/sdhci.c

@@ -2939,12 +2939,17 @@ int sdhci_add_host(struct sdhci_host *host)
 			host->vqmmc = NULL;
 		}
 	} else {
-		regulator_enable(host->vqmmc);
+		ret = regulator_enable(host->vqmmc);
 		if (!regulator_is_supported_voltage(host->vqmmc, 1700000,
 			1950000))
 			caps[1] &= ~(SDHCI_SUPPORT_SDR104 |
 					SDHCI_SUPPORT_SDR50 |
 					SDHCI_SUPPORT_DDR50);
+		if (ret) {
+			pr_warn("%s: Failed to enable vqmmc regulator: %d\n",
+				mmc_hostname(mmc), ret);
+			host->vqmmc = NULL;
+		}
 	}
 
 	if (host->quirks2 & SDHCI_QUIRK2_NO_1_8_V)