Report the legacy fallback behavior for uuid attributes just once
instead of logging repeated warnings for the same condition every time
the attribute is read. The old behavior is too spamy on the kernel logs.

Cc: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Reported-by: Breno Leitao <leitao@debian.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Keith Busch <kbusch@kernel.org>