greybus: use decimal notation for interface and cport ids

Fix up the few places where hexadecimal rather than decimal notation was
used for interface and cport ids.

Note that this includes the endo sysfs-attribute for the AP interface
id.

Signed-off-by: Johan Hovold <johan@hovoldconsulting.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>