Use short options for cmp

In order to be consistent with other uses of cmp and to improve compatiblity
with other implementations, like busybox one, change long options to short
ones.

Signed-off-by: Walter Lozano <walter.lozano@collabora.com>

cmdline/apt-key.in

@@ -314,11 +314,11 @@ is_supported_keyring() {
     local FILEEXT="${1##*.}"
     if [ "$FILEEXT" = 'gpg' ]; then
 	# 0x98, 0x99 and 0xC6 via octal as hex isn't supported by dashs printf
-	if printf '\231' | cmp --silent --bytes=1 - "$1"; then
+	if printf '\231' | cmp -s -n 1 - "$1"; then
 	    true
-	elif printf '\230' | cmp --silent --bytes=1 - "$1"; then
+	elif printf '\230' | cmp -s -n 1 - "$1"; then
 	    true
-	elif printf '\306' | cmp --silent --bytes=1 - "$1"; then
+	elif printf '\306' | cmp -s -n 1 - "$1"; then
 	    true
 	else
 	    apt_warn "The key(s) in the keyring $1 are ignored as the file has an unsupported filetype."