mmc: core: improve mmc_of_parse_voltage() to return better status

Improve mmc_of_parse_voltage()'s return values so that drivers can tell
whether a voltage-range specification was present, and whether it has
been successfully parsed, or there was an error while parsing.

We return a negative errno when parsing fails, zero if no voltage-range
specification is present, or one if a voltage-range specification is
successfully parsed.

No users need modifying as no users check the return value.
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

drivers/mmc/core/core.c

@@ -1204,8 +1204,9 @@ EXPORT_SYMBOL(mmc_vddrange_to_ocrmask);
  * @np: The device node need to be parsed.
  * @mask: mask of voltages available for MMC/SD/SDIO
  *
- * 1. Return zero on success.
- * 2. Return negative errno: voltage-range is invalid.
+ * Parse the "voltage-ranges" DT property, returning zero if it is not
+ * found, negative errno if the voltage-range specification is invalid,
+ * or one if the voltage-range is specified and successfully parsed.
  */
 int mmc_of_parse_voltage(struct device_node *np, u32 *mask)
 {
@@ -1216,7 +1217,7 @@ int mmc_of_parse_voltage(struct device_node *np, u32 *mask)
 	num_ranges = num_ranges / sizeof(*voltage_ranges) / 2;
 	if (!voltage_ranges) {
 		pr_debug("%s: voltage-ranges unspecified\n", np->full_name);
-		return -EINVAL;
+		return 0;
 	}
 	if (!num_ranges) {
 		pr_err("%s: voltage-ranges empty\n", np->full_name);
@@ -1238,7 +1239,7 @@ int mmc_of_parse_voltage(struct device_node *np, u32 *mask)
 		*mask |= ocr_mask;
 	}
 
-	return 0;
+	return 1;
 }
 EXPORT_SYMBOL(mmc_of_parse_voltage);