scripts: Fix shellcheck warnings for checkpatch scripts

- Switching from 'set -e' to 'set -euo pipefail' for better error handling.
- Quoting all variable expansions to prevent word splitting and globbing.
- Replacing legacy unquoted $(...) and $@ with quoted forms.
- Using array-safe idioms where necessary (e.g., "${src_files[@]}").

This patch doesn't change any functionality.

scripts/checkpatch_commits

@@ -1,21 +1,21 @@
 #!/usr/bin/env bash
 
-set -e
+set -euo pipefail
 
-rootdir=$(readlink -f $(dirname $0)/..)
-scriptsdir=${rootdir}/scripts
-base_commit=${1:-master}
+rootdir="$(readlink -f "$(dirname "$0")/..")"
+scriptsdir="${rootdir}/scripts"
+base_commit="${1:-master}"
 
-commits=$(cd ${rootdir} && git log --pretty=format:"%h" ${base_commit}..HEAD)
+commits=$(cd "${rootdir}" && git log --pretty=format:"%h" "${base_commit}"..HEAD)
 err=0
 
-for commit in $commits; do
-	echo "Running checkpatch for commit $commit"
+for commit in ${commits}; do
+	echo "Running checkpatch for commit ${commit}"
 	echo -e "========================================\n"
 
-	(cd ${rootdir} &&
-		git format-patch -1 --stdout $commit | ${scriptsdir}/checkpatch -) || err=1
+	(cd "${rootdir}" &&
+		git format-patch -1 --stdout "${commit}" | "${scriptsdir}/checkpatch" -) || err=1
 	echo -e "\n"
 done
 
-exit $err
+exit "${err}"