mmc: tmio: check mmc_regulator_get_supply return value

mmc_regulator_get_supply returns -EPROBE_DEFER if either vmmc or
vqmmc regulators had their probing deferred.
vqmmc regulator is needed by UHS to work properly, therefore this
patch checks the value returned by mmc_regulator_get_supply to
make sure we have a reference to both vmmc and vqmmc (if found in
the DT).

Signed-off-by: Fabrizio Castro <fabrizio.castro@bp.renesas.com>
Reviewed-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Tested-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>