mmc: host: omap_hsmmc: Do not initialize MMC regulators to NULL on error

Do not initialize MMC regulators to NULL on error in omap_hsmmc driver
similar to what is done in mmc_regulator_get_supply(). This is in
preparation for using mmc_regulator_get_supply() to get MMC
regulators.

Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>