t10-pi: reduce ref tag code duplication

t10-pi: reduce ref tag code duplication

t10_pi_ref_tag() and ext_pi_ref_tag() are identical except for the final
truncation of the ref tag to 32 or 48 bits. Factor out a helper
full_pi_ref_tag() to return the untruncated ref tag and use it in
t10_pi_ref_tag() and ext_pi_ref_tag().

Signed-off-by: Caleb Sander Mateos <csander@purestorage.com>
Reviewed-by: Anuj Gupta <anuj20.g@samsung.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Link: https://patch.msgid.link/20260415210847.1730016-1-csander@purestorage.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>