kbuild: genksyms fix for typeof handling

The tokenizer misses counting an open-parenthesis when parsing a
non-trivial typeof beginning with an open-parenthesis. This function
in include/linux/ceph/libceph.h

static type *lookup_##name(struct rb_root *root,
                           typeof(((type *)0)->keyfld) key)

When instantiated in net/ceph/mon_client.c, causes subsequent symbols
including an EXPORT_SYMBOL in that file to be lost.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michal Marek <mmarek@suse.com>