thunderbolt: fix format string for size_t

The result of "sizeof(struct tb_drom_entry_port)" is a size_t, which
is not necessarily the same as 'long', so we should use the appropriate
%z format string instead of %l.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Andreas Noever <andreas.noever@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>