scripts: never exit 1, always call err instead

this same change has been applied, selectively, to
certain return statements. the general rule is this:
the return statement should only be used to direct
logic within a script, where certain non-errors
states are used to skip certain actions; the exit
command should *never* be used to return non-zero,
except by err(). in so doing, we ensure easier
debugging of the build system

also: strip_rom_image in build/release/roms was
running "continue" when a rom file didn't exist,
despite not being a while/for loop. i make it
return (non-error condition) instead

it's ok for a script to exit 0, where appropriate,
but perhaps a function could also be written for it

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

resources/scripts/update/blobs/mrc

@@ -53,33 +53,33 @@ main()
 	sname=${0}
 	printf "Downloading Intel MRC blobs\n"
 
-	check_existing && exit 0
-	build_dependencies || err "could not build dependencies"
+	check_existing || return 0
+	build_dependencies
 	fetch_mrc || err "could not fetch mrc.bin"
 }
 
 check_existing()
 {
 	[ -f ${_mrc_complete} ] || \
-		return 1
+		return 0
 	printf 'found existing mrc.bin\n'
 	[ "$(sha1sum ${_mrc_complete} | awk '{print $1}')" \
 	    = "${_mrc_complete_hash}" ] && \
-		return 0
+		return 1
 	printf 'hashes did not match, starting over\n'
-	return 1
 }
 
 build_dependencies()
 {
-	[ -d "${cbdir}/" ] || ./fetch_trees coreboot default || return 1
-	./build coreboot utils default || return 1
-	return 0
+	[ -d "${cbdir}/" ] || ./fetch_trees coreboot default || \
+	    err "cannot fetch coreboot/default"
+	./build coreboot utils default || \
+	    err "cannot build cbutils/default"
 }
 
 fetch_mrc()
 {
-	mkdir -p mrc/haswell/ || return 1
+	mkdir -p mrc/haswell/ || err "cannot mkdir mrc/haswell"
 
 	(
 	cd mrc/haswell/
@@ -102,8 +102,6 @@ fetch_mrc()
 
 	printf "\n\nmrc.bin saved to ${_mrc_complete}\n\n"
 	)
-
-	return 0
 }
 
 download_image()
@@ -122,8 +120,7 @@ download_image()
 		return 0
 	fi
 	rm "${_file}.zip"
-	printf "Bad checksum. Recovery image deleted.\n"
-	return 1
+	err "Bad checksum. Recovery image deleted"
 }
 
 extract_partition()