LU-16518 target: fix unused-but-set-variable warnings

LU-16518 target: fix unused-but-set-variable warnings

In tgt_checksum_niobuf(), remove the unused err return code
of cfs_crypto_hash_final() to silence a Clang compiler
warning.

Test-Parameters: trivial
Signed-off-by: Timothy Day <timday@amazon.com>
Change-Id: I6dfe664479d4430c4386d2ff50644e41d91a4c28
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/58183
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Max Wang <wamax@amazon.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Reviewed-by: Oleg Drokin <green@whamcloud.com>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>