EX-7601 obd: add error check in merge_chunk

EX-7601 obd: add error check in merge_chunk

If the lnbs we're trying to merge have an error recorded in
them, then they're not going to be valid input for
decompression, so return an error.

Signed-off-by: Patrick Farrell <pfarrell@whamcloud.com>
Change-Id: I1bf17131cb65106087eb5e72e2700db30c0cc975
Reviewed-on: https://review.whamcloud.com/c/ex/lustre-release/+/53274
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Artem Blagodarenko <ablagodarenko@ddn.com>