nasm: end labels with colon (':')

Labels should end by colon (':'), nasm requires it.

Provide nasm compatibility.  No binary change by this patch with yasm
on {x86_64,i686}-fedora13-linux-gnu.  Few longer opcodes with nasm on
{x86_64,i686}-fedora13-linux-gnu have been checked as safe.

Change-Id: I0b2ec6f01afb061d92841887affb5ca0084f936f