build/descriptors: simplify and fix error handling

main() on top

some parts of the script weren't erroring properly

Signed-off-by: Leah Rowe <leah@libreboot.org>

resources/scripts/build/descriptors/ich9m

@@ -1,6 +1,6 @@
 #!/usr/bin/env sh
 
-#	 Copyright (C) 2020 Leah Rowe <info@minifree.org>
+#	 Copyright (C) 2020, 2023 Leah Rowe <info@minifree.org>
 #
 #	This program is free software: you can redistribute it and/or modify
 #	it under the terms of the GNU General Public License as published by
@@ -16,29 +16,36 @@
 #	along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #
 
-# This script assumes that the current working directory is the root
-# of libreboot_src or libreboot git
-
 [ "x${DEBUG+set}" = 'xset' ] && set -v
 set -u -e
 
-if [ ! -f "util/ich9utils/ich9gen" ]; then
+ich9gen="util/ich9utils/ich9gen"
+
+main()
+{
+	if [ ! -f "${ich9gen}" ]; then
 		(
-    cd util/ich9utils/
-    make clean
-    make -j$(nproc)
+		cd util/ich9utils/ || err "cd"
+		make clean || err "make-clean"
+		make -j$(nproc) || err "make"
 		)
 	fi
-if [ ! -f "util/ich9utils/ich9gen" ]; then
-	printf "build/descriptors/ich9m: ich9gen wasn't compiled. Exiting\n"
-	exit 1
-fi
+	[ ! -f "${ich9gen}" ] && \
+		err "ich9gen doesn't exist"
 
-[ -d "descriptors/" ] || mkdir -p "descriptors/"
 	[ -d "descriptors/ich9m/" ] || mkdir -p "descriptors/ich9m/"
-rm -f descriptors/ich9m/*
+	rm -f descriptors/ich9m/* || err "rm-rf"
 
 	(
-    cd descriptors/ich9m/
-    ../../util/ich9utils/ich9gen
+	cd descriptors/ich9m/ || err "cd2"
+	../../"${ich9gen}" || err "ich9gen"
 	)
+}
+
+err()
+{
+	printf "%s: %s\n" $0 $1
+	exit 1
+}
+
+main $@