move parameter interrupt-parent to optional ones
improve example

Signed-off-by: Stefan Wahren <stefan.wahren@i2se.com>
Statictize local functions
Fix include of wrong header file

Signed-off-by: Stefan Wahren <stefan.wahren@i2se.com>
Fix signed / unsigned compare

Signed-off-by: Stefan Wahren <stefan.wahren@i2se.com>