check: fix Fixes trailer regex

The sed command with the regex fails to keep the sha1 and remove the
commit title from the 'Fixes' trailer. Then the git command fails to
find the commit. A commit with 'Fixes' can not be validated by the
script.
Fix the regex to extract the sha1.

Signed-off-by: Jeremie Leska <jeremie.leska@6wind.com>

Author: jeremie6wind

check-commits.sh

@@ -104,7 +104,7 @@ for rev in $revisions; do
 		if [ -z "$value" ]; then
 			continue
 		fi
-		fixes_rev=$(echo "$value" | sed -En 's/([A-Fa-f0-9]{7,}[[:space:]]\(".*"\))/\1/p')
+		fixes_rev=$(echo "$value" | sed -En 's/([A-Fa-f0-9]{7,})[[:space:]]\(".*"\)/\1/p')
 		if ! git cat-file commit "$fixes_rev" >/dev/null; then
 			err "trailer '$value' does not refer to a known commit"
 		fi