scripts/common-functions: cve2sha: fix multiline output from vulns DB
$ ./scripts/check-kernel-fix -s 5.5 CVE-2021-47181
failes with uknown sha for the given CVE because vulns.git cve_search
returns unexpected multi-line output
$ scripts/cve_search CVE-2021-47181
CVE-2021-47181 is assigned to git id 14651496a3de6807a17c310f63c894ea0c5d858e
f08adf5add9a071160c68bb2a61d697f39ab0758
Filter out the first line only to handle that