fstools: update to HEAD of 2019-07-01 - 1539b5

fstools: update to HEAD of 2019-07-01 - 1539b5

Update fstools to commit 1539b535ac327a3bc599d1ca871e14fd0dc3bba1

git log --pretty=oneline --abbrev-commit ff1ded63..1539b535

1539b53 libblkid-tiny: increment label size to 256
d563f3c libblkid-tiny: fix wrong btrfs label length
3957dd3 block: prevent mount point confusion
9b36dc2 libfstools: avoid false positives when matching devices and volumes

Created with the help of the make-package-update-commit.sh script.

Signed-off-by: Christian Lamparter <chunkeey@gmail.com>