Set blockSize to 512
Set blockSize to 512

This fixes size reported by du, which assumes blocks are given in 512
byte pieces.

cmars/tools,FracturedRetina/go-mtpfs,cmars/tools,wisavalite/go-mtpfs,cmars/tools,wisavalite/go-mtpfs,cmars/tools,FracturedRetina/go-mtpfs,wisavalite/go-mtpfs,FracturedRetina/go-mtpfs