mmc: mxcmmc: fix the default value for available voltages into mxcmci_probe

If available voltages are not given, mmc_regulator_get_supply() function
returns 0 and mxcmmc driver doesn't set a value for ocr_avail mask.

In accordance with the comment in platform_data/mmc-mxcmmc.h,
fix it, assuming MMC_VDD_32_33 | MMC_VDD_33_34 as default value.

Signed-off-by: Matteo Facchinetti <matteo.facchinetti@sirius-es.it>
Reviewed-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>