Increase buffer for sysfs disk state

Increase buffer for sysfs disk state

Bad block support has incremented sysfs disk state reported by kernel
("external_bbl") so it became longer than 20 bytes. It causes reshape to
fail as it reads truncated entry from sysfs.

Increase buffer so it can accommodate the string including all state
values currently implemented in kernel at the same time.

Signed-off-by: Tomasz Majchrzak <tomasz.majchrzak@intel.com>
Signed-off-by: Jes Sorensen <Jes.Sorensen@redhat.com>