encgen.py: fix typo in category, extra i for imm8
encgen.py: fix typo in category, extra i for imm8

Change-Id: I324253caf9e585226959efa1f42dcf227bce5b02
(cherry picked from commit c9bba258f762fcea7e7ddedd170d8e1ee91c8604)

intelxed/xed,intelxed/xed,intelxed/xed,intelxed/xed