fix(st-sdmmc2): check regulator enable/disable return

The issue was reported by Coverity [1]. The return of the functions
regulator_disable() and regulator_enable() was not checked.
If they fail, this means there is an issue either with PMIC or I2C.
The board should the stop booting with a panic().

[1] https://scan4.scan.coverity.com/reports.htm#v47771/p11439/mergedDefectId=374565

Change-Id: If5dfd5643c210e03ae4b1f4cab0168c0db89f60e
Signed-off-by: Yann Gautier <yann.gautier@st.com>
diff --git a/drivers/st/mmc/stm32_sdmmc2.c b/drivers/st/mmc/stm32_sdmmc2.c
index 1a8bd5b..dbdaa54 100644
--- a/drivers/st/mmc/stm32_sdmmc2.c
+++ b/drivers/st/mmc/stm32_sdmmc2.c
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2018-2021, STMicroelectronics - All Rights Reserved
+ * Copyright (c) 2018-2022, STMicroelectronics - All Rights Reserved
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
@@ -157,13 +157,17 @@
 	uint32_t clock_div;
 	uint32_t freq = STM32MP_MMC_INIT_FREQ;
 	uintptr_t base = sdmmc2_params.reg_base;
+	int ret;
 
 	if (sdmmc2_params.max_freq != 0U) {
 		freq = MIN(sdmmc2_params.max_freq, freq);
 	}
 
 	if (sdmmc2_params.vmmc_regu != NULL) {
-		regulator_disable(sdmmc2_params.vmmc_regu);
+		ret = regulator_disable(sdmmc2_params.vmmc_regu);
+		if (ret < 0) {
+			panic();
+		}
 	}
 
 	mdelay(VCC_POWER_OFF_DELAY);
@@ -173,7 +177,10 @@
 	mdelay(POWER_CYCLE_DELAY);
 
 	if (sdmmc2_params.vmmc_regu != NULL) {
-		regulator_enable(sdmmc2_params.vmmc_regu);
+		ret = regulator_enable(sdmmc2_params.vmmc_regu);
+		if (ret < 0) {
+			panic();
+		}
 	}
 
 	mdelay(VCC_POWER_ON_DELAY);