of: Drop duplicate 'the' in of_find_last_cache_level kerneldoc

Delete duplicate words of "the".

Signed-off-by: Deming Wang <wangdeming@inspur.com>
Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20220624011247.1735-1-wangdeming@inspur.com