Cleanup: use ctf_scope_string function to print `enum ctf_scope` vars

Cleanup: use ctf_scope_string function to print `enum ctf_scope` vars

This fixes the following Clang warning:
  ctf-meta-resolve.c:278:28: error: implicit conversion from enumeration type 'enum ctf_scope' to different enumeration type 'enum bt_scope' [-Werror,-Wenum-conversion]
                                  bt_common_scope_string(scope));
                                  ~~~~~~~~~~~~~~~~~~~~~~ ^~~~~
  ../../../../include/babeltrace/logging-internal.h:854:46: note: expanded from macro 'BT_LOGV'
                          BT_LOG_WRITE(BT_LOG_VERBOSE, _BT_LOG_TAG, __VA_ARGS__)
                                                                    ^~~~~~~~~~~
  ../../../../include/babeltrace/logging-internal.h:818:18: note: expanded from macro 'BT_LOG_WRITE'
                                                          lvl, tag, __VA_ARGS__); \

Signed-off-by: Francis Deslauriers <francis.deslauriers@efficios.com>