disas: nanoMIPS: Correct comments to handlers of some DSP instructions

Correct comments to handlers of some DSP instructions.
Signed-off-by: NAleksandar Markovic <amarkovic@wavecomp.com>
Reviewed-by: NAleksandar Rikalo <arikalo@wavecomp.com>
Message-Id: <1551800076-8104-2-git-send-email-aleksandar.markovic@rt-rk.com>