FatFs: Get rid of the union.
FatFs: Get rid of the union.

We'll need first_block_ref for writable mounting.

johnkingsley/aprinter,ambrop72/aprinter,fixator/aprinter,fixator/aprinter,johnkingsley/aprinter,fixator/aprinter,ambrop72/aprinter,johnkingsley/aprinter,fixator/aprinter,ambrop72/aprinter,johnkingsley/aprinter,johnkingsley/aprinter,fixator/aprinter,ambrop72/aprinter,johnkingsley/aprinter,fixator/aprinter,ambrop72/aprinter,ambrop72/aprinter,ambrop72/aprinter,johnkingsley/aprinter