ARM: 7620/1: mmc: mmci: Convert to use mmc_regulator_get_supply

By using the mmc_regulator_get_supply API we are able to do some
cleanups of the regulator code. Additionally let the regulator
API handle the error printing.

Cc: Chris Ball <cjb@laptop.org>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>