Silence compiler warning

warning: passing argument 2 of 'active[(int)i].callback' discards 'volatile' qualifier from pointer target type
Update FatFs to R0.10
fat-provider: separate FatFs FRESULT / CBM errno_t errors

Some FatFs functions depend on the error code of other internal functions,
so making them an alias to CBM_ERROR-ones does not seem to be a good
idea if some information is lost by mapping several FatFs errors to a
single CBM error code (e.g. CBM_ERROR_DRIVE_NOT_READY)
fat-provider: fix directory headline

f_getcwd() from FatFs  0.9 reported <DRIVE:>/Path
f_getcwd() from FatFs 0.10 reports only /Path

Furthermore, paths get preceeded by ".." now
when they exceed 16 characters.