02: Fixup homework assignment

Firstly, move error reporting into create_frames() so that
ERROR_ERRNO() can be used. Then, swap arguments to
posix_memalign() so that separation between frames is increased
to 65KiB. This should crash reliably if there's an error in MMU
implementation.

And finally, introduce and use ARRAY_CARDINALITY() macro.

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>