virSecurityDACSetOwnershipInternal: Don't chown so often
virSecurityDACSetOwnershipInternal: Don't chown so often

It's better if we stat() file that we are about to chown() at
first and check if there's something we need to change. Not that
it would make much difference, but for the upcoming patches we
need to be doing stat() anyway. Moreover, if we do things this
way, we can drop @chown_errno variable which will become
redundant.

Signed-off-by: Michal Privoznik <83d82aaba2eed257f4814b0c239c260c4caaadf0@redhat.com>

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