OpenZFS 9479 - fix wrong format specifier for vdev_id

[behlendorf]

Description

Fix wrong format specifier for vdev_id

Motivation and Context

OpenZFS-issue: https://www.illumos.org/issues/9479
OpenZFS-commit: openzfs/openzfs@20aa447c

How Has This Been Tested?

Locally built.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Performance enhancement (non-breaking change which improves efficiency)
• Code cleanup (non-breaking change which makes code smaller or more readable)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation (a change to man pages or other documentation)

Checklist:

• My code follows the ZFS on Linux code style requirements.
• I have updated the documentation accordingly.
• I have read the contributing document.
• I have added tests to cover my changes.
• All new and existing tests passed.
• All commit messages are properly formatted and contain Signed-off-by.
• Change has been approved by a ZFS on Linux member.

[codecov]

Codecov Report

Merging #7699 into master will decrease coverage by 0.03%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #7699      +/-   ##
==========================================
- Coverage   78.11%   78.08%   -0.04%     
==========================================
  Files         368      368              
  Lines      111830   111830              
==========================================
- Hits        87354    87320      -34     
- Misses      24476    24510      +34

Flag	Coverage Δ
#kernel	78.68% <ø> (-0.06%)	⬇️
#user	67.05% <ø> (+0.02%)	⬆️

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