mmc_da: Queued CCBs need a priority other than CAM_PRIORITY_NONE

Queued CCBs usually are queued at CAM_PRIORITY_NORMAL, unless they are
doing error recovery, or device enumeration of some kind. They should
never be queued at CAM_PRIORITY_NONE, which should only be used for CCBs
that are immediate. For sdda_start_init_task(), we allocate a ccb,
initialize it then use it to talk to the SD/MMC card to query it,
negotiate the speed and lane sizes, etc. Most of these commands are
queued, so use the normal priority.

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