Add default handling to switch and revisit error handling

The Java naming convention claims:
Every switch statement should include a default case.

Revisit all switch statements and add a default case if needed. While
at it check the error handling.

Signed-off-by: Benedikt Spranger <b.spranger@linutronix.de>
Reviewed-by: Bastian Germann <bage@linutronix.de>