bt_field_type_compare(): deep-compare mapped clock classes

bt_field_type_compare(): deep-compare mapped clock classes

Deep-compare mapped clock classes in bt_field_type_integer_compare()
instead of just comparing the pointers. Given the same contexts, two
integer field types which have equal properties and equal mapped clock
classes (not just equal clock class pointers) are considered equal.

Signed-off-by: Philippe Proulx <eeppeliteloop@gmail.com>