Fix for problem in CC2420 read caused by a wrong variable name.

[inode-]

Fix for problem in CC2420 read caused by a wrong variable name usage and a change of the logic.

This error cause a fail read on data from the CC2420.

The bug has been introduced in https://github.com/travisgoodspeed/goodfet/commit/16391a9a0eb80835c1f6bd4c9e0a72053eb511d1

[rmspeers]

This shows a change of i to ret which seems to make sense in this case, however it also has another line which the comment indicates it's unclear why it's needed. Any insight into where this was seen to be helpful, or what happened when testing without it?

[inode-]

I'm pretty sure it was a duplicate check, but honestly after 1 year I don't remember anything. Surely an extra check doesn't hurt ...