mmc: core: Clarify usage of mmc_set_signal_voltage()

The mmc_set_signal_voltage() function is used for SD/SDIO when switching to
1.8V for UHS mode. To clarify this let's do the following changes.

- We are always providing MMC_SIGNAL_VOLTAGE_180 as the signal_voltage
  parameter to the function. Then, let's just remove the parameter as it
  serves no purpose.
- Rename the function to mmc_set_uhs_voltage().

Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Reviewed-by: Shawn Lin <shawn.lin@rock-chips.com>
Tested-by: Jan Glauber <jglauber@cavium.com>
Tested-by: Stefan Wahren <stefan.wahren@i2se.com>
diff --git a/drivers/mmc/core/sdio.c b/drivers/mmc/core/sdio.c
index 261c886..a64a870 100644
--- a/drivers/mmc/core/sdio.c
+++ b/drivers/mmc/core/sdio.c
@@ -642,8 +642,7 @@
 	 * to make sure which speed mode should work.
 	 */
 	if (!powered_resume && (rocr & ocr & R4_18V_PRESENT)) {
-		err = mmc_set_signal_voltage(host, MMC_SIGNAL_VOLTAGE_180,
-					ocr_card);
+		err = mmc_set_uhs_voltage(host, ocr_card);
 		if (err == -EAGAIN) {
 			mmc_sdio_resend_if_cond(host, card);
 			retries--;