mtp & gphoto2: add missing newlines at the end of debug messages

Commit edd777b1e675f9328aa00934651b4763783930a1 modified DEBUG() macro
and, by replacing combination of g_vfprintf(stderr, message, args) and
g_fprintf(stderr, "\n") with a g_logv(G_LOG_DOMAIN, G_LOG_LEVEL_DEBUG,
message, args), caused a lack of trailing newlines in debug messages.

Signed-off-by: Rok Mandeljc <rok.mandeljc@gmail.com>