In order to utilize both swap partitions to balance the I/O load (striping), they should have the same priority. The /bin/swapon command shipped with Maemo is the busybox version that does not support -p option. If you don't have Easy Debian environment installed, download the stock Debian mount package for the armel architecture and extract (-x) the swapon binary from it, and copy it somewhere e.g. /sbin/swapon.debian.