thermal: fix Documentation bullet list warning

Fix bullet list indentation formatting to prevent a docs build warning.
Use same indentation style as other files in this directory.

Documentation/ABI/testing/sysfs-class-thermal:201: WARNING: Bullet list ends without a blank line; unexpected unindent.

Fixes: 80da1b50 ("thermal: Move ABI documentation to Documentation/ABI")
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>