libmount: avoid resolving pseudofs source on update

libmount: avoid resolving pseudofs source on update

Similar to the previous commit, when mounting a pseudofs, trust the
source of the fs, as it cannot be matched to backing device on the
filesystem.

Similar situation, but slightly different bug:

  # mkdir /foo /root/foo
  # echo 'foo  /foo  tmpfs  defaults  0  0' >> /etc/fstab
  # cd /root
  # mount -a
  # mount | grep /foo
  /root/foo on /foo type tmpfs (rw,relatime)

This fixes the pure libmount based mount utility, but the legacy mount
tool will still fail to handle this properly.

Signed-off-by: Dave Reisner <dreisner@archlinux.org>
Signed-off-by: Karel Zak <kzak@redhat.com>