"ARC prefetch metadata accesses:" appears twice in the output.

The first occurrence should be "ARC prefetch data accesses:"

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Alexander Motin <mav@FreeBSD.org>
Signed-off-by: ofthesun9 <olivier@ofthesun.net>
Closes #15427