disas: nanoMIPS: Fix order of some invocations

Fix order of extraction function invocations so that extraction
goes from MSB side to LSB side of the given instruction coding
content. This is desireable because of consistency and easier
visual spotting of errors.

Reviewed-by: Aleksandar Rikalo <arikalo@wavecomp.com>
Reviewed-by: Stefan Markovic <smarkovic@wavecomp.com>
Signed-off-by: Aleksandar Markovic <amarkovic@wavecomp.com>