ENOENT if the option wasn't provided, instead of setting it to 0.
xfs however didn't catch up on this, so it assumed something went bad if
vfs_getopts() sets the error to non-zero, and just returns the error.
Unbreak xfs mount by just ignoring the error if vfs_getopts() sets the
error to ENOENT, as we should have sane defaults.
Reviewed by: kan
Approved by: re (rwatson)
Tested by: rpaulo