Corrected misspelling (Odomoter -> Odometer)

Signed-off-by: Morten Hustveit <morten.hustveit@gmail.com>
Corrected serial baud rate setup

It turns out cfsetospeed and cfsetispeed takes predefined constants rather than
integer parameters.  Instead of passing 115200, we must pass B115200.

Tested: Connected to Arduino after a cold boot; did not run stty
Signed-off-by: Morten Hustveit <morten.hustveit@gmail.com>
Fix odometer update function

There was some weird arithmetic here that could never work.  This change should
make the motors run more smoothly.

Tested: Ran the motors
Signed-off-by: Morten Hustveit <morten.hustveit@gmail.com>