for unknown reasons, multiwrite is busted in usdhc:
sdhc: write error intr 10 stat ff88858e
usdhccmd: need to reset Datinhibit intr 10 stat ff88858e
usdhc: cmd 193a0027 arg 1e5b6b error intr 18010 stat ff88858f
i'm disabling it for now, adding a flag to the SDio struct.