cap brightness at 100%

had an issue where when brightness was at 100%, it claimed it was set at
105%, despite not being possible.

.local/bin/x-brightness

@@ -20,6 +20,7 @@ down) brp=$((brp - AMOUNT)) ;;
 	;;
 esac
 brp=$((brp - (brp % AMOUNT)))
+[ $brp -gt 100 ] && brp=100
 
 brightnessctl set $brp%
 ico=display-brightness-symbolic